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Ozone depletion is the dark side of theCFC experiment. But, for science, there is abright side — the great progress in atmos-pheric chemistry, made over the past 25years, which stems in part from the scientificand political drive to understand CFCs andozone depletion, and in part from the studyof the rapid yet transient rise of the synthetichalocarbons. For example, the earliestmeasurements of CFC-11 envisaged its useas a tracer of air motions9, and it has becomea standard test of global models of atmos-pheric chemistry10 (and also a diagnosticindicator of ocean circulation); the firstmeaningful measure of the mean tropos-pheric concentration of hydroxyl radicals(OH), which destroy CH3CCl3 and HCFCs,is derived from observations of CH3CCl3

(refs 11, 12); CFC pollution events in Irelandare used to calibrate European emissions ofother greenhouse gases13; and study ofCH3Br (a crop and soil fumigant) has shownus the importance of the ocean in determin-ing the atmospheric residence time of a solu-ble trace gas, and has resulted in revisionof the concept of ozone-depletion potentialfor short-lived gases14.

What new opportunities will the secondphase of the CFC experiment provide?Through its latitudinal gradient, the decay ofCH3CCl3 will give us a measure of thenorth–south hemispheric difference in OHconcentrations, plus a long-term record ofpossible OH trends. And, after sources ofCFC-11 have diminished sufficiently, itsatmospheric decay will provide us with the

first accurate lifetime for a CFC, and thenorth–south differences at the surface willmeasure hemispheric asymmetry in strato-sphere–troposphere exchange. It is seren-dipitous indeed that CFCs and relatedhalocarbons have provided, and will contin-ue to provide, some of the benchmarks ofprogress in atmospheric chemistry.Paul J. Fraser is at CSIRO AtmosphericResearch/CRC Southern Hemisphere Meteorology,PMB 1, Aspendale, Victoria 3195, Australia. e-mail: paul.fraser@dar.csiro.auMichael J. Prather is in the Earth System ScienceDepartment, University of California, Irvine,California 92697-3100, USA.e-mail: mprather@uci.edu1. Prather, M. et al. Nature 381, 551–554 (1996).

2. Montzka, S. A. et al. Nature 398, 690–694 (1999).

3. Oberthur, S. Production and Consumption of Ozone-Depleting

Substances 1986–1995 (Deutsche Gesellschaft für Technische

Zusammenarbeit, Berlin, 1997).

4. Velders, G. J. M. & Madronich, S. in Scientific Assessment of

Ozone Depletion: 1998 Ch. 11 (UNEP/WMO, in the press).

5. Butler, J. H. et al. J. Geophys. Res. 103, 1503–1511

(1998).

6. Fraser, P. J. et al. J. Geophys. Res. (in the press).

7. Executive Committee of the Multilateral Fund for the

Implementation of the Montreal Protocol China’s Halon Sector

Strategy (UNEP/OzL.Pro/ExCom/23/11, 21 October, 1997).

8. Wuebbles, D. & Calm, J. Science 278, 1090–1091 (1997).

9. Lovelock, J. E. Nature 230, 379–381 (1971).

10.Prather, M. et al. J. Geophys. Res. 92, 6579–6613 (1987).

11.Lovelock, J. E. Nature 267, 32 (1977).

12.Prinn, R. et al. Science 269, 187–192 (1995).

13.Simmonds, P. G. et al. Atmos. Environ. 30, 4041–4063

(1996).

14.Butler, J. H. Geophys. Res. Lett. 21, 185–189 (1994).

15.Prinn, R. et al. in Scientific Assessment of Ozone Depletion: 1998

Ch. 1 (UNEP/WMO, in the press).

16.Kurylo, M. et al. in Scientific Assessment of Ozone Depletion:

1998 Ch. 2 (UNEP/WMO, in the press).

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664 NATURE | VOL 398 | 22 APRIL 1999 | www.nature.com

100 YEARS AGOThe Groundwork of Science; a Study ofEpistemology. By St. George Mivart. Thechief definite conclusions which aredrawn are that it (the universe) cannotconsist of one kind of energy only, that itis impossible that intellect can have beenevolved from mere physical force, andthat animals show no signs of latentintellectuality. It is further insisted “thatthe portion of truth which we are able toattain to in our investigations of thecosmos, is but an unimaginably smallportion of the whole”; a statement whichwill, we imagine, not be seriouslychallenged by workers in science. To thelatter, viz. the science workers, Dr. Mivartdevotes some attention in the concludingpages of his book. The narrowing effectof extreme specialism upon the mind isan undoubted evil ... . But there is theopposite evil of becoming diffuse to theextent of a practically useless attenuationof the mental faculties.From Nature 20 April 1899.

50 YEARS AGOMr. H. E. Hadley, well known as theauthor of many elementary text-books ofphysics, died on March 6, at the age ofeighty-two. Mr. Hadley had lived rather aretired life. He was appointedheadmaster of a small science school inKidderminster, where he combined withphysics a lectureship in chemistry. Inthose days, physics was considered ofless importance than chemistry; but Mr.Hadley was always at heart a physicist.… Mr. Hadley was a contemporary of SirRichard Gregory and H. G. Wells at [TheRoyal College of Science, London], andfrom his training there and associationwith C. V. Boys he acquired a specialgenius for making his physical apparatus.His teaching equipment at Kidderminsterwas largely of his own making, and itwould seem that this gave physics anadded attraction to his students.

We regret to announce the followingdeath: Mr. Will Hay, well known as anactor and also a distinguished amateurastronomer, on April 18, aged sixty. From Nature 23 April 1949.

Many more extracts like these can be found inA Bedside Nature: Genius and Eccentricity inScience, 1869–1953, a 266-page book edited byWalter Gratzer. Contact Lisa O’Rourke.e-mail: l.orourke@nature.com

Figure 1 Ozone-destroying tracegases now and in the future —observed6,15,16 and predicted4

atmospheric chlorine loading,in parts per billion of Cl, fromvarious halocarbons. a, CFC-12;b, HCFCs; c, halon-1211 (effec-tive Cl). d, Halon-1211 emis-sions calculated fromatmospheric measurements and from a production-basedemissions model6.

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