DISCUSSION-S. MAL ON FORMS OF STRATIFIED CLOUDS 42r

the lapse-rate in the unstable stratum was due to radiation into space from the upper surface, combined with warming of the lower surface by radiation from the earth. Such clouds appear to occur more often in the morning and evening than at midday.

With reference to Dr. Whipple’s argument that Helmholtz waves may coexist with this pattern, he thought the argument against that was that one frequently got ,patterns of both lines, and it was impossible to see any difference of character between them. He referred to a n occasion when. the sky was covered with strips in one direction, a periodic formation. which developed in them, and at the end of ten minutes the lines were at right angles to the former and had the same kind of periodic pattern upon them.

With regard to Mr. Durst’s change of direction with height the stream is thin and with one velocity a t the bottom and another at the top, there is only one shear between them whether the directions are the same or not. We had habitually produced horseshoe patterns in the laboratory without any change of direction.

Thunderstorm at Stoner Hill, Petersfield, August 5, 1931. During a very severe thunderstorm on the afternoon of August 5 , a

fir tree less than 50 yards from this house was struck by lightning. The damage to the tree was slight but rather curious; a strip of bark just under 8 feet long was taken off; above this there was a crack about zf feet long, ending at the top in a very small abrasion of the bark where presumably the lightning entered. N o other damage is apparent. The question arises, was the tree struck a t this point? It seems unlikely as the lightning would have had to have travelled a t a considerable angle to get under the branches. I t seems more likely that the lightning came down the tree from the top on the wet surface; there was a deluge of rain a t the time; 2.15 inches fell in 55 minutes, and the hyetograph showed that at the height of the storm half an inch of rain fell ih four and a quarter minutes. The tree must have been running with water which would have afforded a good conducting path. Lower down some slight crack, already existing perhaps, may have made an easier path through the wet cambium layer, with the result that some of the bark was blown off. (See Plate XV.) C. J. P. CAVE.

Normal Daily Temperature of the Air at Greenwich The following table, supplied by the Astronomer Royal, gives the

normal daily mean temperature of the air derived from go years’ observa- tion (1841-1g30) at the Royal Observatory, Greenwich, together with a similar series, for oomparison, derived in the same manner from the 65 years 1841-1905.

In computing the table, the actual mean values derived have been smoothed arithmetically, i.e., each quantity given in the table is the mean of the actual values for five successive dates, of which the third corre- sponds to the tabular date; and in computing the mean values February 29 has been systematically ignored. The practical result of ignoring February 29 is, of course, a further slight smwth i ig of the means.

Attention may be drawn to the effect of the number of comparatively mild winters and cool summers of the present century on the means for the longer period, which in some instances show a difference of almost a whole degree Fahrenheit from the 65 years’ mean. A secondary minimum about February 10-12, and a secondary maximum about August 12-14 are features of both sets of mean values.

August 12, 1931.