JANUARY lO, 1895] 



NATURE 



249 



seen and learnt to recognise many varieties of shape and 

 form, arising possibly from real ditierences of structure, 

 which require distinctive appellations, and make the 

 description somewhat cumbrous. To quote the entire 

 list of subdivisions would occupy no small space. Leaving 

 out of the question fog, which is itself divided into three 

 classes, we have the clouds of interfret, inversion, and 

 inclination, each subdivided into five different varieties. 

 To this list, large as it is, must be added several ad- 

 ditional subdivisions, all presenting marks of dissimi- 

 larity, and it is suggested, typical of special states of 

 weather in different portions of the globe. Each of the^e 

 classes is described at considerable length, and many of 

 them are admirably illustrated, both by coloured plates 

 and photographs. We have recently reproduced 

 (Nature, vol. xlix. p. 342) some admirable specimens of 

 rloud photography, due to S. Manucci of the Vatican 

 Observatory, illustrative of the distinctive characteristics 

 of cloud formation. Mr. Arthur Clayden has secured 

 some very admirable specimens, worthy to be classed 

 with those of the Italian artist. We give in Figs. I and 

 2 the reproduction of the same cloud (cumulo-nimbus) 

 after an interval of ten minutes, in 

 which the shifting character of clouds 

 is well illustrated. The truthfulness 

 to nature is shown very conspicuously 

 in an evening picture of the same 

 variety of cloud (Fig. 3). 



But the important question is, will 

 illustrations, however carefully exe- 

 cuted, give to persons of ordinary 

 intelligence that insight into cloud 

 structure which enormous experience 

 has given to Mr. Ley, and enable 

 them to discriminate with facility and 

 certainty between the various classes ? 

 The author raises the objection, not 

 as existing in his own mind, but as 

 having been suggested to him by 

 others whose opinion he values, that 

 the classification here presented is 

 too complex. We would respectfully 

 associate ourselves with those who 

 have suggested this doubt. Mr. Ley's 

 contention is, that greater simplicity 

 of description might induce a larger 

 number of observers to contribute 

 something, but that the luiliic of the 

 whole mass of such observations would 

 be of small amount, through however 

 long a space of time they were con- 

 tinued. The main value consists in 

 the evidence it affords of the different forces at work in 

 the air, and its consequent trustworthiness as a weather 

 guide, and on this point there will be many different 

 opinions. The same description of cloud does not pro- 

 gnosticate the same weather in all countries, or at all 

 times in the same country. The method and cause of 

 development are as important as the character of the 

 cloud itself. Cumulus may sometimes be the promise of 

 a fine day, or prove the precursor of a shower. A man 

 who "forecasts'' by the clouds alone, is in the same 

 position as a man who relies on the indications of a 

 wheel barometer. He simply considers one variable in 

 a very complex result. But Air. Ley looks forward to a 

 time when every man shall be his own "weather pro- 

 phet," and when every individual and institution may 

 be provided with weather telegrams and the means of 

 correct and intelligent interpretation. In the multitude 

 of counsellors so created there may be wisdom ; there 

 will certainly be confusion. 



Waiting tor this consummation, it seems most desir- 

 able that the same kind of cloud should be called by the 

 same name by all observers ; and simply having regard to 



NO. 1315, VOL 51] 



the main divisions, it will be admitted on all hands that 

 this amount of progress has not yet been effected. We 

 have then to consider whether this book, valuable as it 

 is, will promote this end, and we are afraid that it will 

 prove an edged-tool to beginners. To the advanced 

 student it can easily be understood that this work is most 

 welcome, but there still seems necessary a simpler system 

 to serve as an introduction for the tyro. Mr. Ley may 

 very well say that he addresses himself only to skilled 

 observers, and to some this will be a sufficient defence, 

 but this skill is not easily acquired, and we look 

 for a graduated system, along which a student may 

 advance confidently and scientifically. Abercromby and 

 Hildebrandsson recognise and would recommend a classi- 

 fication of ten divisions, a system of which we believe 

 the author disapproves. Captain Wilson Barker would, if 

 we understand his arrangement correctly, still further 

 simplify this system, and therefore it does not seem im- 

 possible to lead the student along an easy incline in 

 which he would gradually accumulate experience, rather 

 than plunge him at once into the subtleties and pitfalls 

 which Mr. Ley prepares for the beginner. 



Fig. 



-Cutnulo-niTnbus (evenini^). 



It is easy to understand how difficult a problem was 

 submitted to the International Meteorological Committee 

 when they were asked to adopt and sanction a uniform 

 nomenclature of clouds, and how prudent they were in 

 declining the invitation (N.\'lURi:, vol. xxxviii. p. 491).' 

 Simply having legard to the fact, that meteorologists are 

 generally agreed that the same cloud forms and cloud 

 structure are to be met with all over the world, it would 

 seem that an International Congress was admirably 

 adapted for the settlement of such a scheme. But it was 

 felt, and the feeling will be still more general after the 

 perusal of Mr. Ley's book, that our knowledge of the 

 physical and structural process of cloud formation is in 

 a progressive state, and therefore final classification im- 

 possible. Mr. Ley would probably be the last to con- 

 sider that his book possesses the element of finality. He 

 has not only learnt and taught much, but he has also 

 learnt, better than most of us, how much more there 

 is to learn. 



W. E. P. 



1 This subject is slill cngiRing the attention of .in International Congress 

 (Seep. 185.) 



