Daily rainfall at the royal observatory, Greenwich, 1841-1903

QUARTERLY JOURNAL OF THE

ROYAL METEOROLOGICAL SOCIETY - VOL. XXXVI.] OCTOBER 1910 [No. 156

DAILY RAINFALL AT THE ROYAL OBSERVATORY, GREENWICH, 1841-1 903.

By WILLIAM CARPENTER NASH.

[Read May 25, 1910.1

THE primary object of this analysis was the determination of the average daily run of the rainfall, with subsequent development of the accumulated materials into monthly and annual periods. The total number of calendar days in the years under discussion, amounts to 23,009, of which 9930 are classed as rain days, distributed throughout the years of observation as shown in Table I. In this enumeration it is to be understood that a rain day is considered to be one on which the rainfall amounted to -005 in. (at least), but in the calculations all smaller recorded amounts have been taken into account. In the cases of deposition from dew, frost, or fog, the small amounts derived from those sources have usually been merged into the next succeeding rainfall, but in every case they have always been taken into consideration.

The daily rainfalls having been extracted from the printed records were arranged in sequence on convenient forms, and the means for each nominal day taken throughout the period. In the few cases in some of the earlier years in which the references have been made to different gauges, care has been exercised in referring the whole of the records to one standard. And for facilitating the process of calculation with these numerous entries, the values were split up into three groups, each twenty-one years in length, extending from 1841 to 1861, 1862 to 1882, and 1883 to 1903, thus giving greater certainty in dealing with so large a mass of figures, the separate means being afterwards combined to obtain values for the whole period. These mean values are given in Table 11.

It will be seen that considerable variation exists from day to day in the values in this table, especially in the summer and autumn months.

Y

TABLE I.-&~ONTHLY NUVBEB OF RAIN DAYS AS EECORDED AT THE ROYAL OBSERVATORY, GREENWICH, IX THE 63 YEARS, 1841-1903.

_,- - 22 4

19 I9 9 24 I4 24 IS 8

15 27 17

12

22 I 0 9 9

I 8 I 0

I 0 I7 I7 7 19

I3

16

I 0 21

I1

12 22 14 17 18

'3 13

18 13 23 I4

23 14

6 I7 9

I 2

I2

I2

11

20 22

'5 I 8 15 I9

17

14

14 24

rg.1

I 1

I0

I 1

- -

14 I7 6

I0 I2 8

13 I3 '5

7 13 15 9 6

17 13

17 I7 15

I4 16

I2

I 0

I2

I

19

7 8 16 I3

16 '5

6 19

16

13 6

14 I7 16

17 8

I0

I1

I 2

I2

I S

I 0

I 0 I0

I2 IS

23 13

'7

6

I4

I7 16

1.5

15 17

22

21

I2

22

I 0

3 3 16

13 9

I7

16 IS 19

18

I 0

X I

22

I0

:d 1s I3

14.2

I2 - -

1841 1842 1843 1844 1845

1847 1848 1849 I850 1851 1852 '853 I854

I 846

::;i ::$ 1859 I860 I861 1862 1863 I 864 I 865 1866

1869 1870 1871 1872 I873 I874 I875 1876 1877 1878 I879 I 880 1881 I882 I 883 I 884 1885 I 886 1887 I888 1889 1890

3

1 0

I 0 I2

8

16 I7 16

17 9

15 16

15

18

5

I0

20

20

20

11 21

7 I7 16

16 I 7 I8

I4 '5 I8

15

17 13 23

I 1

21

20

I2

I 1 12

9 9

I9 15 15 22

14 I1 I2

I 0

19 I?

9

15 16 8 9

14 17

I 1

I 0 I 1

I2 I 0

I d I 1 I 0 3 6

'3

6 9

19 18 I 3

I 2

I 1

I2

'5 16 6

16

15

8 6

3 I4 6

6

8

IS

10

I0 22

20

I2

10

10

21 21 I0

10

20

'5

15

I2 , I 8 13

15 15 17

14

20

I0

20 I 0 I2

I 0 22 I1 I2

so 17

8 7

13

15

I3 I 8 '3 5

13 9

24 15

16 16 IS 15

I4 16 19

X I

I 0 I 1

12

I 0

I 0

12

21 I2 I7 '5 20 I8 9

19 IS 18 16 17

9

I3 9

19 8

rz 16

I40

20

10

- -

16 16 7

I3

19 14 I2 29 8

7 '5

I 1

11

I 0 12 I 0 I 0 I 1

I 1 8

25

9

13 S

I1

14 14

7

18 3

15

22

21 I 0

20

10 I2 I 2

I2 16

I 8 5

17 9

I4 8

16 I 0 10

I3 8

6

5 7

15 I2 7

I 1

5 I 0 22 15 4

'3 I 1 9

I0 19 15 '9 5

'5 14 18

9 17 6 5

I2

21

I 1

I 1 22 I2 9 5

15 12.3

22

-

-

8 14 5

IS I3

I9 15

14

16 7 4

I2

21

2

3 I 1

I3 13 6

13 9 4 7

13 2 0 I 0 I 0 6

18 13

8 9

I2 12

20

:i 16 8

13

I S 9

I 0

I 2 I 1 I4 17 I4 8

3 '3

16

I 0

I2 I 0

I 0 20 I 1

'3 7

11

!2.0 - -

8 I4

I3 8

16

5

I 0

22

I 0

I1 21

I 2 17

9 7 9 5 7

23 15 17 14

5 1 5 7 5 9 4

I 8 '5

I 0

I 1 I 1 I 1 I 0 7

14 20 20

9 19

' d

'2 7 9 3

16

I4

I4 8

14 I 2 I1

X I

a

6 17 9

' 5 I0

1 5 1 5 '3 19

6 17

15 16 4

17 15

I3 9

7

I2

I2

I 0

12

I 0

20 12

3 3

9

6

I1

12

2 I 0

I7 16 9

16 8

15 9

I9 24

I9 16 16 5

13

26 16 I8 17

18

16 7 7 9 8 5 8

'3

10

I2

I 0

I2

22

I2

II ' 16 17 11

I 0 16 '5 I 1 7

I 8 17

14 4

I 1

11 I 1

11 14

I 1 I 0

6

14 I 0

I2 I 1

13 17 I9

6 17 15

8

20

I 0

10 10

I2 9

14 '5

16

17 '5 '5

6

22

I 1

20 I 1

12

I 0 19 17

'3 '3 14 14

9

19 18 '3

18 18 9

'5

I 1

I2

21

8 15

16

I 1 I 0

I1 22 I 1 9

14

15 I4 17

I2

I2 21 I 0

I2 16

7 6 I2 14 14 13 5

23 16

5 15 6 6 8

15

I s g I . 1802 I I

15

'9 9

I7 8

18

21

22

'2.4 ' '3.2 11.6 , 12.6

N.B.-These numbem are given as printed in the abstract tables in the Greenwich There are a few discrepancies in the earlier volumes which cannot Xeteorological Volurnes.

be satisfactorily explained.

NASH-DAILY RAINFALL AT GREENWICH OBSERVATORY 311

They were therefore subjected to a numerical smoothing process by taking the means of each five consecutive values, and repeating the process with the resulting means. The smoothed values thus obtained are given in Table III., but aa there were rather large irregularities still remaining, the numbers were plotted on a diagram, and a mean drawn by hand to

TABLE II.-MEAN DAILY VALUE OF TEE OBSEEVATION~ OF RAINFALL MADE AT TEE ROYAL OBSERVATORY, GREENWICH, IN THE 63 YEARS, 1841-1903.

-

Aug.

- h y s of the Month.

-

Dee. Mu. June. Fcb. Jan. I

I Apr. ' May. Nov.

I 2

3 4 5 6 7 8 9 I 0 11 I 2 13 14 15 16 I7 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jeans -

.06 I

_.

,052 -062 .076 .072 -074 449

1 Suitable allowance M d e for Febraary 29th in taking the monthly m a n .

represent the general run of the curve cleared from its minor irregularities (Fig. 1).

The ordinates, aa read from this mean curve, are considered to represent fairly well the average daily rainfall. They are given in Table IV.

The monthly means at the foot of thb table differ slightly from those in Table II., tbe variations arising naturally from the overlapping of the monthly values in the curve, which is of c o m e unavoidable.

It hae notbeen considered necessary in this paper to followMr. Gleisher's

^.

DU

fMO

Ll

JAM

UA

RV

N

IIU

AR

V

MA

RC

H

AP

RIL

M

AY

J

UM

L

JULY

A

UG

US

T

LIPT

ENBI

R o

crn

wn

M

OV

LUB

ER

D

cctu

cmu

JAN

UA

RY

5 IS

25

5 15

25

5

15

251

5 I5

25

5 15

25

5

I5 I5

S

I5 25

5

15 I5

S

I5

25

5 I5

I5

5 I5

75

5 IS

I5

5 15

25

S

IS C

S . ,..

I

'.

. .

:n

.

FIo.

l.--

Lie

an

Dai

ly f

liiuf

all

at th

e Royal

Obn

erva

toiy

, Qre

enw

ich,

184

1-19

05.

The

Dot

ted

Lin

e re

pres

ents

the

adop

ted

Ave

rage

Val

ues.


example, by printing the whole of the daily records ; but should fuller information be required with regard to particular cases, reference should be made to the annual.volumes of Gremwich Meteorological Obsnvatians. The monthly totals for the whole period were given in my former paper ‘ I Nonthly Rainfall a t the Royal Observatory, Greenwich, 18 15-1 903.” 2

TABLE IIL-DAILY SMOOTHED VALUES OF TEE GBEENWICH RAINFALLS AS DEDUCED FROM THE 83 YEARS’ OBSEBVATIONS, 1841-1903.

/‘Days of the i . Month.

I 4 3

6

9 I 0 I 1 I2 ‘3 14

i :s

I 2 27 28 29 30 31

Means --

The aggregate rainfall, 1624.206 ins., recorded in these 63 years represents a mean daily amount throughout the whole period of *066 in. The mean monthly values vary from *091 in. in October to .048 in. in March. The total number of rain days in the period as given in Table I. is 9920, the mean fall per rain day is therefore -154 in. (Fig. 2).

J. Olaisher, “ On the Fall of Rain on every Day of the Year, 1815-1889,” Proc. Jiet. SOC. vol. 6, 1870.

* W r t . Jmcm. Roy. Met. Soc. vol. 30, 1904, p. 291.

314 NASH-DAILY RAINFALL AT GREENWICH OBSEBVATORY

TABLE IV.-APPROXIMATE AWRAQZ DAILY RAINFALL AT TEE ROYAL OBSERVATORY, GREENWICH, A S DEDUCED FBOY 63 YEARS' OBSXRVATIONS MADE IN THE YEARS 1841-1903. -

%E Month.

I Ocr Nov.

--

I I I !

June. July. ~ --

in. ~ in. -068 s o 6 8

I / Jan. i Feb.

I S p t . Mu.

in. I in. .082 I

2

3 4 5 6 7 8 9

I 0 X I I2 '3 14 15 16 I7 I8 19 m 21 22

23 zq 25 26 27 28 29 30 31

HCalU

- -078 -072 -076 -067 , -076


The relative percentages of rainy and rainless days in each month are as follows :-

1s41-13ti1.

Months.

January February March . April . May . June . July .

1862-158?. Isa~-l90.?.

Monthly Percentage. Rain Days. Rainless Days.

% % 47.6 52.4 44.0 56.0 42.4 57.6 40.0 60.0 39.8 60.2 38.7 61.3 40.5 59.5

Date.

1852, Jan. 13 1858, Feb. 14 1851, Mar. 15 1851, Apr. 20 1849, May 28 1852, June 9 1853, July 14 1843, Aug. 23 1859, Sep. 26 1857, Oct. 22 1861, Nov. 13 1860, Dec. 30

Xonthly Percentage. b i n Daya. Rainless Days. Mouths.

% % A u p t . 41.7 58.3 September . 41.1 58.9 October . 4P.8 51.2 November . 46.8 53.2 December . 45.8 54.2

56.9 - --

Year. . - 43.1 - - -

.haunt.

ins. 1.607 .77I 990 2.510 x,;x8 1.456 3.6661 1.788 1.354 1.224 .855 '950

Excessive Rninfnlls.-In Table V. the heaviest daily falls recorded in each month of the year, in each of the three 21-year periods are giveu.

Date.

1866, Jan. X I 1869, Feb. 12 1870, Mar. 4 1878, Apr. X I 1878, May 7 1863, June 19 1867, July 26 1865, Aug. 23 1S80, Sep. X I 1880, OCt. I 0 1864, Nov. zq 1876, Dec. 23

Amount.

ins. 4359 4 1 5 4 8 5 ,804

1.280 1.703 2.491 1.441

1.193 1.370

1.007 1.196

hfUNTHS. - Amount.

January . February . March . April. . M a y . . June . . July . . August . September October . November. December.

ins.

.880 1.520 -8Yo 1.135 1.305 2.455 2.280 1.295 2.510 1.287 .925

1.120

Date.

1886, Jan. 6 1890, Feb. 15 1896, Mar. 18 1885, Apr. 16 1886, May 24 1888, June 26 1888, July 30 1888, Aug. I 1883, Sep. X I 1894, Oct. 30 1887, Nov. 3 1898, Dec. 7

During the 63 years there were 94 occasions on which the rainfall exceeded 1 in. in the d3y, as given in the following Table TI. Sixty of these falls ranged between 1.00 in. and 1-25 in. ; 1 9 between 1.25 in. and 1.50 ins. ; 8 between 1.50 in. and 2 ins. ; 6 between 2 ins. and 3 ins. ; and 1 fall exceeded 3 ins. The 7 falls exceeding 2 ins. in amount were :-

2.280 ins. on 1843, August 23 2.456 _ _ 1853. Julv 14 - _..

2.465 1903; July 23 2.491 ,, 1888, July 30

I 1 3.666? ,, 1867, July 26l

2610 ins. on 1857, October 22 2.510 ,, 1878, April 11

The recurrence of heavy falls on, or about, certain days is remarkable. In this connection it may be pointed out that excessive falls occurred four

With reference to the rainfall recorded on July 26, 1867, to which some degree of suspicion is attached, it may be mentioned that check observations of thu fall were d e by the gauges at the heightr of 10 feet and 22 feet above theground, giving 3.19 ins. and 9.01 ins. respectively. Reducing these values to corresponding ground values (naing the reliible ratios for July, deduced from the observations made in the years 1871-1880), the followhg values are obtained ; 3-27 ins. and 3.32 ins. ; @ping a mean value, 3.30 ins. It would seem therefore that the value given above should be diminished by about one-tenth of its recorded ~ N O U U ~ . but this is purely hypothetical.

316 BASH-DAILY RAINFALL AT GREENWICH OBSERVATORY

times on August 23 ; three times on June 10, July 11, August 17, and October 30; and twice on June 5 and 13, July 23 and 26, September 10 and 11, and October 22.

TABLE VI.-DAILY RAINFALLS EXCKEDINQ OXE INCH IN AMOUNT.

ins. ' 1 1.12 1889. June 10 1.25 1' 1896 ,, 10 1.61 !i 1903 ,,

ins. 1.37 I .04 1.32

::$ 2.45

I .06 367 1.28 1.03 1.28 2.49 1.17 1.19

I .08 2.46

2.28 1.81

1.w 1.26 1-79

I.jZ 1.10

1.10 1.01

I .02

- 7 ' % IOU1 ,, l j

1.17 ~

1.23 I 1861 1887 " ,, 22 3

-- ins. I 44 1.15

1.20 1-10 1.29 1.14 1.35 1-37 I .og I .og 1.03

I .os 1.42 r .02 1.13 2.51 I .06

I .05

1.14

1.19 1.05

i&

1.10

1.11

1-12

1.22

1.01

1.m 1.01

I .06

I .2g

1.20

Frequency of the Rainfall.-The distribution of the amount of rsinfall throughout the year has been mainly dwelt upon in the preceding summaries, but no roference has been made hitherto to the subject of its frequency. It is true that in Table I. an abstract of the monthly number of rain days recorded in the whole period is given, but this conveys no information with regard to the distribution of the rainfall- frequency in the course of the months. A rearrangement of the rain days as referred to each nominal day is shown in Table VII:

The day with the maximum number of rain days to its credit is December 5, with 41 days, which is equivalent to 65 per cent of the total number of days of observation ; the days with least number of rain days are April 18, 19, June 27 and September 13, on each of which the recorded number of days of rainfall is 17, equivalent to 27 per cent of the possible number.

The numbers in Table VII. being subjected to a numerical smoothing


proceae similar to that applied to the rainfalls (as already described), and the daily resulting values divided by the number of the years of observa-

TABLE VIL-DISTRIBUTION THBOUDHOUT: THE YEAB OF THZ TOTAL NUXBER OF RAIN DAYS A8 REFERRED TO EACH NOMINAL DAY, RECOXDED IN TEE 63 YEARS, ~1841-1903.

Days of the Month

Day. I 2

3 4 5 6 7 8 9 I0 I 1 I2 13 I 4 15 16 I7 I8 I 9 20 21 22

23 24 25 26 '7 28 -9 30 37

iggrcgate iumber of

Days.

Or the 14 proportionally

- J a n -

Days 31 31 34 30 34 28 31 25 33 26 30 31 33

24 27 36 32 30 30 23 32 27 32 32 29 31 29 28 31 37

'29

22

-

-

- Feb.

Days 34 39 28 27 28

34 31 28

28 26 27 33 29 27 23 23 31 29 25 28 30 23 24 27 28 29

-

22

21

- MU.

Days 37 27 28

24 24 26 33 3' 28 23 25 27 25 23

26 I9 29 25 32 28 26 23

26 27

-

22

22

::

- April

Days 23

2.5 23 26 26 29 28 30 28 25 29 30 26 26 24 I7 I7 23

26 28 24 24 28

30 25

-

2

22

22

21

- May - Days

21 21

29 23 23

25 3' 32

30 28

22

21

21 22 21 28 27 30 27 26 23 30 25

26

25 31 28 I 9

20

22

21 -

- Juh

Day 26 25 25

24 27 26 26 31 26

23

I8

30 23 26 30 25 23 28 30 33 26 32 27 28 25

-

21

22

21

22

22 20 - 91

- Oct

Day! 29 32 25 30 28 38 36 34 33 34 35 26 27 33 32 36 25 28 35 28 32 33 30 29 29 34 27 31 3' 51 23

'54

-

-

- atercalar days in the 63 yean, 184;-15.03, g were rainy : and these havl this tabre throughout the month of Fehruvy in order to maintain the t

- Nov.

Days - 30 31 35

27 27 25 25 31 29 24

35 32

26 26 29 29 26 34 38 38 28 3' 29 33

2

f S

3

- 84 - :en d ncc.

- Dee. - Days 33 24 30 33 41 35 34 32 28 27 27 29 30 31 31 29 29 37 24 25 26 28 I8 2 0 21

25 30 33 31 28 26 - 95

ributed -

tion, a mean percentage of frequency of rain days throughout the year is formed, which is given in Table VIII.

Disregarding minor changes, the following salient points would appear to be indicated in this table of frequency, v iz :-first maximum, at or about January 31; first minimum, April 19; second maximum, August 6; second minimum, September 13 ; third maximum, October 8 ; third minimum, December 23. The corresponding periods referring to the rainfall as shown in Table IV. are:-January 15, March 31, July 30, September 10, October 17, and December 22. Referred to the day of the year these epochs are :-

Frequency. Rainfall. Fimt Maximum . . . . Net day 15thday. First Minimum . . . . 109th ,, 90th ,, Second Maximum . . . . 218th ,, 212th ,, Second Minimum . . . . 256th ,, 253rd ,, Third Maximum , . . . 281st ,, 290th ,, Third Minimum . . . . 357th ,, 356th ,,

318 NASEI-DAILY RAINFALL AT GREF3WICH OBSERVATORY

It will be seen that a fairly good agreement is established between these epochs, the principal disagreement being in the spring when the frequency shows a tendency to lag behind the rainfalls (see Fig. 3).

It is to be regretted, for statistical reasons, that no regular account is kept of duration of the rainfall ; but perhaps this would be a task too exacting for the ordinary observer, and such determinations could only be obtained with certainty from self-recording instruments.

.

TABLE VIII.-XEAN PERCENTAGE OF F i c ~ u u e u c ~ OF RAIN DAYS THROUGHOUT THE YEAR

39

Days of ie Month. ~ Jan. --

47 46 45 44 43 43 43 43 44 44 45 46 46 43

I 2

3 4 5 6

5 9 10 I 1 I? '3 I4 15 16 17 18 I9 20 21 22 23 24

2 27 28 29 30 31

52 53 53 52 5 0 48 47 46 46 47 48 48 48 47

' x i 48 , 49 j ;: 49 48

! 47 1 46 47

1 46 46

1 46 ~ 45 ~ 45 45

I 46 I 47 47

! 47 ' 47

I :: 1 47 47

i 48 I 48 i 48 49

i 5 C 1 5'

5 2

- ieb. - % 52 5' 49 47 46 45 45 44 44 43 43 44 44 44 44 43 42 42 43 43 43 43 43 42 43 44 45 45

- dSr. - % 46 45 43 42 42 42 43 44 44 43 42 41 40

;8 38 39 39 41 42 43 43 44 43 44 43 43 43 42 42 42

- Lpr. - % 41 41 40 40 40 41 42 43 44 45 44 44 44 43 4' 39 37 35 34 35 36 38 39 40 40 41 40 39

5;: - 40

---.- Means. 47 44 42

- 81 ay.

% 37 37 37 38 39 40 41 42 43 42 42 40 39 39 40 41 42 42 42 42 41 40 39 39 39 39 40 40 39 38 37

40

-

- -

une. 1 July. ! Aug. i Sept. ---- % 36 37 38 40 41 42 42 4' 40 39 58 38 38 39 39 40 41 41 41 40 39 38 37 36 35 35 36 36

g3 I

39 -

x 39 39 39 39 40 41 4' 41 41 40 38 37 36 36 37 39 40 4' 42 42 43 44 45 46 46 45 44 42

% 39 41 43 45 47 49 48 48 46 44 41 40 39 39 40 40 41 41 4' 41 40 ,4I 41 41 41 41 40

% 40 41 4' 42 42 43 42 4'

35 34 33 33 34 36 38 39 4' 42 44 44 45 45 45 45 45 46 46 47

$

Oct. I Nov. 1 Dec.

% 47 47 48 49 5 0 52 53 54 53 52 5' 5 0 49 49 49 49 48

47 47 ~ 49 I :; Yearly Mean-43.17 per cent, confirming the mun annual percentzqe of rain days already given.

The rain days in the whole period, with registered falls not exceeding half an inch, amount to 94 per cent of the aggregate number of rain days. In each of the 21-year periods the relative percentages are 93'6, 93.3, and 95.0 respectively, showing consistent agreement throughout. A further step in elucidating the distribution of the rainfall was made by arranging the falls under different heads of amount. To eliminate the effect due to the unequal length of the different months, the values have been reduced to percentages of the total monthly amounts, and these are exhibited in Table IX., and serve to show clearly


the decrease which takes place in the summer and autumn months in the number of days of small falls.

TABLE IS. -PERCENTAGES OF RAIN DAYS CUS8IFIED Ix ACCORDANCE WITH ~ I ~ A L L h O U N T 9 , DEDUCED PROM OBSERVATIONS MADE IN THE 63 TEAFLY, 1841-1903.

3-9 4.2 6.7 5.7 6.3 7.8 5'4

Percentage of Rain D a p

2.8

1.9 3'0 4.7 3.4 5'2

2.2

r t m u y s

uz

days

22

g P

23

Year.

--

1877 1893

21 1848

23 26 29 23 27 24

23

1860 1888 1848 1896 1853 1872

1868

--

- 05 in.

f ? 10 in.

M O N T H 5 - 10 in.

'4 a0 in.

- 20 in.

'4 30 in.

~ e s s '.as in. than to 325 in. j .o5 in. --

21.4 , 13.0 24.9 1 12.5 25.2 , 12.1 24.7 ' 15.6 --

% 20. I 18.0 19.4 16.9 19.5 17.4 15.9 15 .5 14.9

15.7 I 4 9

12.2

% 20.0 20. I 21-6 23.0 19.0 18.3 I 8-0 17-7 20. I 17.4 19-5 23.2

% 9.5 9.8 7'2 9 3

10.9 10.7 10.9

I 3.0 11.3

10. I

10.2 10.2

January . . February . . March. . . April . . . May . . . June . . . July . . . August . . September . . October . . November . . December . .

16.6 1 9 8 10.2 : 5.8 1 3.1 , Year . . . I 23.6 I 14.7

Table X. gives a recapitulation of the monthly means and extremes for the whole period.

TABLE X.-&[ONTHLY MEANS AND EXTREMES OF RAIXFALL ASD NUMBER OF &IN DAYS FOR THE 63 YEARS. 1841-1903.

Rainfall. Rain Days.

Months.

-- January . February . March . . April . .

May . .

June . . July. . . August. . September October . November.

December.

Year.

- I 880 1891 1852

1855

1896

1895

1899

1897

1873

I 864

1865

1867

Year.

- days 14.8 12.4

13.2 12.0

12.4

11.6 12.6 12.9 12.3 15.1 14.0

I42

1877 I 866 1851 1878

1865

1903 I 888 1878 1896 I 880 1852

1876

- 1 9 3 -

ins. 1.88 1.48 1.49 1.57

1.92

2.02 2.43 2.36 2.16 2.83

1.84

2.21

1858

1852 1852

1848

I 887 1869 I 864 1865 I 842 1867 1851 1857 1873

1857

days 5 3 3 2

3

3

5

4 5

2

I

Year . . 16.38 I 864 !&+-I9 112 1858 157.5

320 NASH-DAILY BAIXFALL AT GREENWICH OBSERVATORY

Dronglits.-As supplementary to the preceding tables of excessive rainfalls, it has been deemed desirable to present a brief statement bearing upon the droughts experienced in the same period. Adopting Symons’s definition of an absolute drought 89 “ a period of 14 (or more) consecutive days without rain,” it is found that in the 63 years- 1841-1903-there were 103 periods, aggregating 1773 days, conforming to that standard, thus giviiig an average duration per drought of 17.2 days. The mean aruiual number of droughts is therefore 1.63, with an average duration per annum of 28 days. During the six months in the year with sun North of the equator, the average annual number of droughts is 1.06, and mean annual duration 18.4 days; and in the months with the sun South, the average number is 0.57, with a mean duration of 9.7 days. The years with longest periods of drought were :-

Yumber. Total Duration. JIean per Drought. 1865 . . . . . 5 96 days. 19’2 days. 1830 . . . . . 4 75 ,, 18.7 ,, 1 S i O . . . . . 4 67 ,, 16.7 ,, 1899 . . . . . 3 63 I , 21’0 ,, 1387 . . . . . 3 58 :, 19‘3 ,,

The distribution of droughts throughout the year is shown in Table XI.

TABLE SI.--JIONTHLY SIXMARY OF DEOUCBTS RECORDED IX THE 63 YEAEE, 1841-1903.

’ Tow1 Number 1 Aggregate Mean Duration I ofDroughu. per Drought. I Durat’on- i MOSTHS.

I January . . 1 6 February . 6 March. . . , I 0 April . . . ’ 7 May . . . 1 3 June . . . 13 July . . . 13 August . . 10 September . . I 1

October . . 5 November . . 1 December . . 1 a

__-

days. ‘5.3 17.3 19.9 17.7 17.2 18.4 16.0 18.7 16.0 15.2 16.7 ‘5’5

Other subjects of interest which have received attention may be briefly noticed, they include :-( 1) determination of relation of rainfall to the sun’s declination ; ( 9 ) discussion of the variation of the rainfall at the equinoxes and solstices, and comparison of the falls according to the seasons; (3) examination of the popular rainfall-myth relating to St. Smithin’s day, etc.

1. The rainfall in the six months ranging between March 22 and September 23 (with the sun North of the equator), a total period in the 63 years of 11,718 days, aggregated 771.833 inches on 4718 rain days, thus giving a moan fall per calendar day for the period, of *066 inch, and a mean per rain day, of -164 inch. With the sun South of the equator (September 24 to March 2l), a total period of 11,291 days, there were


5202 rain days with an aggregate rainfall of 752-373 inches;-the mean fall per calendar day was therefore a067 inch, and *145 inch per rain day. The difference due to the Bun's position is not significant.

FIO. 3.-Mean Daily Rainfall and Percentage of Frequency.

2. With regard to the rainfall a t the equinoxes and solstices, it has been thought desirable to confine the enquiry to the 21 days immediately surrounding each epoch; thus for the vernal equinox (March 21) the mean value for the 21 days, March 11 to 31, is considered to represent the value for that epoch; for the summer solstice, June 21, by the mean of the falls from June 11 to July 1, and similarly for the autumnal equinox, September 23, and the winter solstice, December 21.

The results are as follows :-

h'fEAN RAINFALL AT THE EQUINOXES AND SOLSTICES. 31em Rainfall Mean Fall

per Day. per Rain Day. : ill. 1 lin.

Vernal Equinox . . . . . . '046 '111 SummerSolstice. . . . . . .067 *175 Autumnal Equinox -072 '170 Winter Solstice . . . . . . '056 -128

The corresponding results for the seasons are as follows :-

. . . . .

idem ILinfnll Mean Fall per Day. per Rain Day.

in. in. Spring February

March 17){ April } Summer (Mean day {:%} . . . . '069 *174 June 14). July

. . . . *080 '182

(Mean day March . . . . $051 .121

. . . -065 *138

322 NASH-DAILY RAINFALL AT GREENWICH OBSERVATORY

As exception may possibly be taken to the months selected to represent the seasons on the ground of their non-accordance with the months usually accepted, it may be explained that they were adopted in order to obtain periods with mean dates corresponding roughly with the dates of the equinoxes and solstices.

3. The fallacy of the popular belief in the “ St. Swithin’s ” legend has been repeatedly pointed out, and has received ample confirmation by the result of this investigation.

Yet another subject to which consideration might have been devoted, is the influence exerted upon rainfall by the direction of the wind, but it has not been found possible to carry out this enquiry, on account of the materials relating thereto not being immediately available.

The greater part of this paper being in a measure supplementary to my former paper which terminated with the yew 1903, it has not been considered expedient to extend the scope of this enquiry beyond that year.

[This paper contained several other Tables which are not printed herewith.]

DISCUSSION.

Mr. W. W. BRYAXT thought that the statement that the daily ra infa l ls were extracted from the printed records was misleading. For many years, from 1849, the 24 hours in the Greenwich volume were taken to end at 9 p.m. Therefore, if the printed figures were taken, the same period of 24 hours had not been taken throughout the whole of the paper. He noticed that in Table V. several of the figures given came into this period, and that the figurea did not agree with the Greenwich volumes, hence he inferred that the author had corrected for the differeuce of epoch. But on April 20, 1851, given as the wettest day in April for 21 years, the figures in the volume were *70 in. on that day, and ‘03 in. on the following day, and by no obvious arrangement could *880 in. be obtained from these figures. Another point open to criticism was that Mr. Nash, after taking the numerical smoothing in groups of five, waa not satisfied with the curve,. but pro- ceeded to hand-smooth it. The effect was to make August appear wetter than July. In the comparison with regard to rain-days, p. 317, “Frequency of Rainfall,” one curve was hand-smoothed and the other not, so the comparison was unfair. He thought that the note at the foot of p. 315 was not justified. There was strong probability that the figures were right. Reference to Mr. Nash’s previous paper (Qua7tcrZy Journal, 1904) shows that he regarded all the figures for 1867 and 1868 as doubtful, and probably in excesa of the truth, but no definite reason, such as incorrectly graduated measuring-glass, was suggested. The remarks on the present paper were made without reference to thie point ; the inference to be conveyed being that, in the speaker‘s opinion, the reason given in the present paper was insufficient to justify the alteration of the printed figures. The different height of the gauges did not prove the figures wrong. The rainfall was measured in two portions, some before 10 a.m., the rest before 10 p.m. The discordance between the ground gauge and the 10 feet was proportionately p t e r (nearly 20 per cent) in the eecond and drier period ; while the discordance between the ground gauge and the 22 feet wrta proportionately the same in both perioda It was probable that the rainfall was spasmodic. Aa regards droughts, the present definition was a period of more than 14 consecutive days without rain, so that a period of exactly 14 days

DISCUSSION-DAILY RAINFALL AT GREENWICH OBSERVATORY 323

without rain wa excluded. The modification would considerably alter the figures given. The treatment of February 29 in Table VII. also appeared exceedingly arbitrary, to say the least of it.

Mr. F. J. BRODIE said that he was glad M i . Bryant had called attention to the percentage emoothing. This was useful to a certain extent, but if too much were done it got rid of the distinctive features. Looking over the figures there were certain periods which might be regarded as those during which there was a strong tendency for rain to recur. Towards the end of July, for instance, this tendency disappeared in smoothing the figures. He himself would prefer the unsmoothed curve. The pencilled curre gave but little more than the average monthly rainfall ; all the distinctive features, which would be shown by the rainfall aa originally calculated, were completely hidden. On p. 315 the author aaid, “The recurrence of heavy falls on certain days is remarkable.” On August 23 falls exceeding 1 inch occurred four times He himself did not consider this remarkable, aa during such a long period some such coincidence was to be expected. He thought it a pity the paper was not extended to the year 1905. The previous paper had only extended to 1903, but this one might have included the 65 years’ mean. It waa 180 to be regretted that the heaviest fall of rain quoted was open to doubt.

Mr. C. SALTER aaid that several references had been made to Mr. Symons’s definition of an “absolute drought.” This definition waa originally drafted in the aame form aa it w a given in Mr. Nash’s paper, namely “ Perioda of 14 or more consecutive days abaolutely without rain,” but in 1887, owing probably to the excessive number of instances which it was found necessary to tabulate in that year, the definition was revised and changed to “ Periods of more than 14 consecutive days absolutely without rain.” It has stood substautially unaltered eyer since. The effect of this change waa to reduce the number of absolute droughts tabulated by approximately 50 per cent. There is, of course, no special virtue in this particular period ; it was selected for want of a better reason, aa giving on the average one drought per year for the neighbourhood of London. Having once been selected, it is undoubtedly desirable that the same definition should be adhered to in all caees, and if this is not done the whole value of the table for comparative purposes is lost. Mr. NBsh stated in the early part of his paper that ‘‘ in some of the earlier years, in which the references have been made to different gauges, care has been exercised in referring the whole of the records to one standard,” but he did not add any statement as to the means used for the purpose of referring them. In the absence of any statement to the contrary, it must be assumed that the method used was that of proportioning by means of a factor determined by comparison of the overlapping portion of the two records. For standardising monthly or annual totals of rainfall this method might be safely utilised ; but with daily values i t waa dangerous, because in different types of weather the gauges might give readings varying enormously in relation to one another on individual &ye, and these variations might be of the most erratic nature. It WIU desirable that a statement as to the method employed ahould be included in the paper. Another point to which criticism might well be directed is that portion of the paper in which the author deals’ with “other subjects of interest which have received attention.” The rubjecta mentioned muet be considered by no m e w the most suitable ones which could have been selected for study by means of the rainfall record at a single station. Accidental irregularities, dependent on factors other than such large general circulations as could arise from the cause9 examined, interfere enormously with individual records, and, unless the general rainfall over a large area could be considered, no advantage could be derived from the investigation which could in any wy.compensate for the labour involved in it Mr. Nash had, however, presented in a concise form an extremely valuable mass of

324 DISCGSSION-DAILY RAINFALL AT GREENWICH OBSERVATORY

observational matter which should prove of the greatest use, and had subjected it to a thorough process of digestion.

Mr. E GOLD said that bir. Nash had extracted much valuable information. He considered this paper to be but one step in the direction of a large work to enable investigations to be carried out on a larger s d e as to vanationa in the weather. Perhaps Mr. Nash might make it clem a t the head of Table 11. that the mean of the obaervations of rainfall was the total rainfall divided by the total number of days in the period discuwd. He was particularly interested in a peculiar feature of the curve, the minima shown for September and March. In both the smooth and rough curves the relation was apparent. In working last year on the variation of the advective region in the c o m e of the year, he had wme across a relation that in March, April, and September it waa reached at the minimum height. I t was interesting to find that a t the same time they got the minimum rainfall at Greenwich. The evidence was not, so far, sufficient for the two things to be connected, but it waa suggestive. Similar investigations should be carried out in other placea He thought Mr. Nash was to be con- gratulated on this paper.

Colonel H. E. Rawsos said that i t was difficult to appraise a paper such as this one at its true value when it first made ita appearance. In this respect i t resembled a baby. The poeeibilities were enormous, and the author certainly deaerved thanks for the labour he had bestowed on ita preparation. One of the important facts which it had brought out, waa the seasonal periodicity which was evident in Table IIL Such periodicity must be sharply defined to enable such a curve to have been obtained. I t is noticeable that minima appear a t the June and December solstices, and about the March and September equinoxes. The maximum in the h t five days of July and the first two of August was of particular interest to him, as he had noticed rain at this time during the rainless season at certain stations abroad, at which he had been quartered. Having in his mind the seasonal migration of the anticyclonic belta and their component system, in both hemispheres, he could not but believe that the same cause would ultimately be found to explain thia phenomenon everywhere. At Greenwich the mean monthly rainfall for July and August was second only to that of Octo-ber, and he had reasons for thinking that the rainfall there of these months often determined whether or not the rainfall of the year would be in excess or deficit of the mean. On testing this point with the aid of the data given by the author in his previous paper of 1904, an interesting result was obtained. Writing down successive ea and da, according as each of the years from 1815 to 1903 was in excess of the mean or showed a deficiency, the several months of the year being treated in the same way, they were compared with one another and with the year. I t came out that in one eeries of 20 Fern August only differed from the year twice. The eeriea lasted from 1860 to 1879, and was represented by the following es and ds respectively :-

e d e d d e e e e d d d e d d e d e e e for the year, I 1

e d e d d e e e e d d d e e d d d e e e for August Only the years 1873 and 1875 do not agree. This might only be a coincidence, though rather a remarkable one, if it were not traceable ale0 in Momman’s analysis of the Edinburgh meteorological elements from 1766 to 1896.’ By a further coincidence the last year, 1879, was identical with the last year of a cycle of excessive Nile floods, which, aa Colonel Rawson baa pointed out to the Society, aeem to be correlated with the oscillation of the southern anticyclonic belt Instead therefore of following the author‘s plan of dividing the 63 years into three periods of 21 years, he had pnrsued the enquiry dividing it into

“The Meteorology of Edinburgh.” By Robert C. Mossman. Part 2, Fmns. Boy. Soc. Elin. 39, part 1. No. 6.

DISCUSSION-DAILY RAINFALL AT GREENWICH OBSEBYATORY 325

periods of 19 years, and carrying it back to 1815, a total of 89 years. I t happened that the year 1903, which was the last year investigated by the author, was also the year when he had reaeon to believe that the southern belt reached ite highest latitude south. There waa therefore a special interest in analysing the rainfall a t Greenwich according to the periods which seemed to have some significance both in the rainfall of the southern hemisphere, and in the intensity of the Nile flood. The fimt point that waa brought out was that though the rainfall at Greenwich for the 19 years 1828-46, waa very similar to that for the 19 yeara 1847-65, viz. 464.47 ina and 462.32 ina respectively, that for 1866-84, when measurements were more accurate, was largely i n excess of that for 1885-1903, viz. 482.76 ins. and 438.02 ins. respectively. The total rainfall however for the 38 years comprised by the h t two periods is 926.79 ins., and by the laat two periods 920.78 ins. These figures indicate that in any analysis of Greeuwich rainfall a period of 19 years may be quite insufficient to lead UB to any correct conclusions. He asked the author if the p t difference in the total precipitution during his second and third periods of 21 years had shown itself in his investigation, and in what way 1 In the southern hemisphere there had been a similar difference observable between some of the meteorological elements during the periods 1866-84 and 1885-1903, the source of which he had traced in a paper read before the South Mrican Ansociation to a displacement in an east and west direction of the Australian anticyclone from its mean eeesonal positions. A similar displacement was indicated to be taking place in the seaaonal positions of the permanent anticyclones affecting the British Ides during the years 1881-91, which he brought to the notice of the Society i n 1898. Arctowski’s recently published researches into temperature variations over large a r e a from year to year, show that of the 10 years 1891-1900, which he haa examined exhaustively, the year 1893 was by far the coldest of them all over very large and widely separated a r e a of the globe This waa the very year when the anticyclonic belt of the southern hemisphere waa found to have reached one end of its oscillation and to be nearest to the equator, aa theory based upon the low temperature Arctowski found prevailing over the globe would suggest that it should be. Many of those present remember the extraordinary drought during the spring of 1893 in these islands, an account of which Mr. Brodie brought before the Society in November of that year. He found that it was largely explained by the almost conatant prevalence of large anticyclonic systems over us. Arctowski’s chart for the year ehows that there wug a great deficiency of heat in a large area to the east of xu, and this would account for anticyclonic systems hugging the land longer than usual, before being driven into mid-atlantic by the increasing temperature of the land surface. The seasonal progressive movement of anticyclones over our a r q modified by variations in the temperature from year to year of large are= to the eastward of us, would afford a plausible explanation of the reawn for the existence of the mean curve of average daily rainfall, which the author brings to our notice. I t might be thought that variations in the excessive monthly rainfall of October would have a greater effect upon the total for the year than an excess or deficiency in June, July, or August. If October‘s rainfall is analyaed in the aame way as August’s, the correspondence is not quite as close. There are 59 years out of 89 in which if the niinfall in August is deficient or in excess of the mean, the total fall during the year is deficient or in excess of the mean also. In the case of October there are 55 ; and no such agreement in consecutive years as occuw in the case of August. We sometimes find the variations in the rainfall of April and the year agreeing in as many as eight consecutive years, and the correspondence between April-a month of very small raintall-and the year is closer than between October and the year. There are 56 years in which the occurrence of a deficiency or excess in this

2

But this is not so.

326 DISCUSSION-DAILY BAINFALL AT GREENWICH OBSERVATORY

month is followed by a deficiency or excesa in the total rainfall of the year. Whether the correspondence which is found to exist between April and August in 50 out of the 89 yeam is of any significance remains to be seen, but in its annual variations the rainfall of Edinburgh in these two months shows some correspondence also, which may not be entirely a coincidence. The fact that one just follows and the other just precedes the equinox is deserving of notice when we remember that the analyaie of the yearn 1881 to 1891 showed that the path followed by the centre of high pressure varied its latitude with the sun'a declination, and was found over our islanh more frequently in June, that is a t the time of the summer solstice, than in any other month. These facts which arise out of the author's paper seem worthy of the attention of the Society, at a time when the data reapecting the seasonal migration of the anticyclonic system in the southern hemisphere are enabling ue to recognise more fully the similar action going on in the northern.

Mr. R. H. Hoogle~ obeerved that the full line in diagram 1 was already a smoothed one. He was not prepared to condemn the author for carrying on the smoothing process further. One wanted to smooth away points and kinks which were purely accidental, but the trouble was to know which were accidental. I t was clear that the simple averages given in the first table were not su5ciently smooth, and therefore mme amount of smoothing had to be done. It also seemed equally clear to him that the dotted line was over-smooth, as it clearly hid a great many variations which it was desirable to have recorded. But it was not easy to decide what was the correct amount of smoothing to be done. Mr. Hooker also thought that the various calculations as to the average duration of droughts of more than 14 days were rather meaningless, inasmuch as 14 days waa a purely arbitrary basis and the figures would be completely altered if any other baais were taken. He was rather curiou, however, to know what was the longest drought on record.

Mr. J. HOP~INBOX drew attention to Mr. Nash's definition of a rain-day as one on which at least '005 in. of rain fell. Although deprecating the reading of a gauge to thousandths of an inch, he considered the author to be correct in this definition. Moet, if not all, the few observers who read to thousandths, he said, made a far greater number of '005 entries than of any other thousandth, showing their e m r of observetion to be greater than their attempted precision of reading, while those who only read to hundredths took special care with an apparent -005 to see whether it were above or below it, and should be taken as nil or the next higher division, ensuring a more accurate result in the reduction to hundredths and the enumeration of raindays than if they read to thousandths, and their recorda of -005 were varioualy treated by different compilers, as they were sure to be in the absence of a definite and generally accepted rule. But in reading to hundredths a measurement which appeared to be exactly *005 had to be provided for, and his own rule had been to consider it as *01 and therefore as a rain-day ; for in such a case they might be certain that, owing to loss in the rain which wets the inner surface of the gauge and evaporatee h m it, more than .005 in. actually fell. This was not the practice of Dr. Mill, BO that Mr. Nash's figures would not correspond with those in British Rainfd, giving a greater number of rain-days, as also, as already pointed out, a greater number of absolute droughts.

Mr. W. C. NUH, not having been present at the Meeting, has furnished the following comments upon the discussion :-

blany criticisms were levelled agaimt the adoption of 14 days as the minimum standard for au absolute drought. It is'agreed that there is no special virtue in the 14 days period, but it appeared to the author that this period had been judiciousIy adopted by Symons, and that it well served its purpose as a starting point for reference. Conversely it has been held by

DISCUSSION-DAILY RAINFALL AT GREENWICH OBSEaVATORY 321

Chambers that “ nothing less than a month of 30 daye should be regarded ad a condition of things to which the term ‘drought’ should be applied.” I t mmt be confessed that many of the objections advanced to the “Symons” period are somewhat vague and indefinite, the only tangible point to be met being that suggested by Mr. Salter, who considered that the omission of the simple period of 14 days would have the effect of “reducing the number of absolute drougl~t~~ by about 60 per cent,” and by Mr. Bryant, who thought I‘ that the modification would considerably alter the figures given.” The author finds that the actual reduction caused by leaving out the 14 day periods would amount to 25 per cent only. If Mr. Chambers’s scale were adopted there would be only one case in the 63 years left as a representative drought, viz, the great drought recorded in 1893 (incidentally referred to by Col. Rawson as the ‘I extraordinary drought of the epring of 1893”), which extended from March 18 to April 16 (a period of 30 days). Presuming that Mr. Hooker’s inquiry as to the longest drought on record refers to the London district, this period will perhaps satisfy that inquiry.

Another point which received considerable attention, and which had been dealt with somewhat adversely, related to the subject of smoothing the meat curve. The author takes exception to many of the views expressed by the Fellows with regard to the value of smoothing. Mr. Bryant’s contention that the effect of hand-smoothing had been to make “August appear wetter than July’’ is a false deduction, as this effect obviously arises from the introduction of the values in the earlier and later months. It appeared to be considered by many Fellows that the smoothing of the curve was objectionable, as tending to hide its distinctive features, overlooking the fact that the aim of the author was to deduce an approximate daily average. To a certain extent the greater inequalities were eliminated by the numerical smoothing, but it appeared to be essential to smooth out the minor irregularities by the method adopted by the author.

Various remarks dealing with matters of detail may be dismissed more or less briefly. The variation in the termination of the day in certain yeam WBB

not considered important as regards this discussion, and not likely to affect the general result. The reference to the discrepancy between the vulue 0.70 in., printed in the Greenwich volume as the rainfall for April 20, 1851, and the value given i n the paper is perfectly just ; but a closer investigation of the Royal Observatory records would have shown blr. Bryant that the value given in the volume wae the amount recorded on the Library roof, a t the height of 22 ft. above the ground, ihereas the value given in the paper was proportionnlly increased to conform to the ground standard. There are many similar caaes in the earlier volumes, and in my reduction the daily records by the Croaley gauge (as reduced to ground values) have been used as far as possible. The Crodey gauge waa planted near to the Standard gange, but with its receiving surface 15 ins. higher, and the differences between the monthly totals by the Crosley and Standard gauges were usually not great during the critical yeara involved. With reference to the note relating to the rainfall recorded on July 26, 1867, which Mr. Bryant considera to be not justified,” it may be remarked that it WBB not likely that the author would have taken the extreme course of caating doubt upon the values for the yeara 1867 and 1868, without strong justification. Mr. Bryant says that ILno definite reason, such as incorrectly graduated memuring- glasa, was suggested.” It was conaidered by the author that it would be im- proper to advance such a suggestion aa baaed alone upon his personal recollection, but it is a fact, however, that a measuring-glass, reserved solely for use with the daily ground gauge, waa condemned and put out of use, although no note can be found in the Observatory records aa to the time at which this took place. The reason given in the former paper (Quwttly Journal, vol. 30, p. 294 ),based

328 DISCUSSION-DAILY RAINFALL AT GREENWICH OBSERVATORY

upon a critical examination of the relation between the gauges, was deemed con- clusive evidence. It is to be seen, also, by reference to the Greenwich volume for 1868, that attention had been directed at the time to the discrepancy between the two ground gauges, and the values for the monthly gauge in that year were. not published, aa a slight leak waa found in the gauge ; but this does not explain the discrepancies between the gronnd values and tho= given by adjacent gauges, shown more especially in the 19 months from June 1867 to December 1868 (inclusive). I do not think that there is any foundation for Mr. Bryant‘s suggestion that the rainfall waa ‘‘ probably spasmodic,” but this could be settled by reference to the ori& weather notes.

A slight alteration in the heading of Table 11. will perhaps meet Mr. Gold‘s wish that it should be clearly conveyed that the daily means given in the table are derived from the aggregate rainfall for the day divided by the total number of days in the period.

It will be scarcely necessary to enter into the somewhat wide field of speculation initiated by Col. Rawson as arising out of the paper; and with regard to hia inquiry as to whether the great difference in the total precipitation during the two periods 1866-1884 and 1885-1903 had been noticed, it may suffice to direct Col. Rawson’s attention to the remarks made by .the author, in his former paper, with reference to two contrasted periods of eight wet and dry years which fall within the period8 quoted.

Local Winds in the South of France. The Bulldin & la soci&d LangucdociGnnc de Gebgraphie (Tome 32, Deuxibme

trimeatre, 1909) contains an article by E. de Martonne on the peculiarities of a wind known in the provinces of Aquitaine and Languedoc under the name of “ vent d’autan ” or “ vent marin.” Observations refer, up to the present, only to the months of October, November, and December 1908, $0 that the conclusions drawn therefrom must not necessarily be extended to the whole year. The wind is an East wind, and haa diflerent characters locally, being called marin ” where it is humid, cool, and of comparatively little violence, and “autan” where it is relatively hot and violent. Like the mistral, the autan is especially known for its destructive violence, but the force is very variable in both time and space. Thus, on the one hand, even during the most violent winds there are moments when the wind drop to a calm, and, on the other hand, places only a mile or so apart may be affected very differently 89 regards the violence. At Labrespy, for instance, situated in the zone of the most’violent autan winds, high velocities are rarely registered, but 2 kilometers away is R road where carriages are liable to be precipitated into the valley, and where pedestrians have to lie flat on the ground. The autan, while dependent on the distiibution of atmospheric pressure for its occurrence, evidently owes its violence to topographical circumstances, and from the great l o d dflerences in its strength may be appropriately designated a topographical wind. The surface inequalities retard or accelerate the air-movernent, and there are spots in the valleys where the wind is described by the inhabitants as dropping down from the heights like a cataract. The autan is doubtless of the nature of the fohn of the Alps, and the marin is converted into the autan in Haut-Langnedoc by topographical features. . The marin is apt to bring falls of snow in winter, which are much dreaded by the foresters of the Montagne Noire. The snow is so thick and heavy that the over-laden branches of the trees are often broken, and the same effect is produced by the rimedepositing fogs which are common in winter. Replanting is rendered di5cult, and the continued extension of heathland over the littleelevated crests of the Montagne Noire is perhaps partly attributable to this cauee.-Geogmphical Journal, June 1910.

Documents

Daily rainfall at the royal observatory, Greenwich, 1841-1903