248 



NA TURE 



[January 10, 1895 



THE STUDY OF CLOUD> 



THIS monograph has been long and anxiously ex- 

 pected by all who take an intelligent interest in the 

 advance of meteorology, and recognise the long and 



V\ '.. I. — Cvinui'.' r; ;t ■ i->. 



profound study that the Rev. Clement Ley has made of 

 this subject. It is with great regret that we notice that 

 the preface is signed by a member of his family, and 

 that the zealous and energetic watcher of the clouds has 

 not been able to see his own work 

 through the press. 



We have in this book to do em- 

 phatically with Mr. Ley's own obser- 

 vations, his own theories of cloud 

 structure, and his own nomenclature. 

 Although the author acknowledges in 

 the preface the valuable assistance 

 that he has received from the works 

 of other writers, it is curious to notice 

 how seldom in the text these authors 

 are referred to by name. One cannot 

 help feeling that it would have added 

 much to the interest and the instruc- 

 tive character of the book, if Mr. Ley 

 had systematically drawn attention to 

 the work of those who have laboured 

 with scarcely less industry than he 

 has in this department, if he had ex- 

 hibited the points of difference from, 

 and support given by, other observers, 

 such as .Abercromby, llildebrandsson, 

 Weilbach, and a host of other authori- 

 ties, who seem sometimes almost 

 ostentatiously ignored. It will be seen 

 that Mr. Ley does not offer anything,' 

 approaching a history of (he subject, 

 either on the theoretical or observa- 

 tional side. Opening with a prelimin- 

 ary chapter on the atmosphere and 

 the movements of vapour-laden air, 

 we have the general principles of cloud formation 

 explained. Although we have been accustomed to 



1 "Cloudland: a Study on the Structure and Characters of CIoudK." Dy 

 Rev. W. Clement Ley, fl.ondnn : SLinlord, i^g* ) 



think that moisture condensed into cloud can only be 

 driven or rolled about in a limited number of ways, 

 and hence but few really distinct varieties of cloud 

 can be formed, our author subdivides the process of 

 cloud formation under several heads. The process which 

 he terms " interfret " seems very 

 nearly allied to the Luftwogen of 

 Helmholtz, though there is no mention 

 of this authority in the text. Mr. Ley 

 states that when approximately hori- 

 zontal currents of air dilTering in velo- 

 city and direction move over one 

 another, an intermingling of the par- 

 ticles will result, accompanied by 

 whirls, ripples, and waves, varying in 

 size and shape according to the 

 velocity and direction of the current. 

 This effect he attributes to friction, 

 and this seems to be the chief differ- 

 ence between him and the German 

 physicist, who sees a more complex 

 problem in the mixing of two fluids 

 of different specific gravities. If the 

 colder current is uppermost, the re- 

 sulting action is called " interfret '' ; 

 if the warm moist current is above, 

 then "reversed interfret." To clouds 

 formed by the descent of moist par- 

 ticles through warmer and denser air, 

 the term " inclination '' is applied, 

 and the final nomenclature adopted 

 rests on subdivisions of these classes 

 uf formations. 



An adequate nomenclature of clouds 

 has long been, and we think it may 

 be said, is still, a desideratum. Luke Howard's 

 terms still survive, and after nearly a century's 

 use cannot, and will not, be entirely superseded. 

 Stratus, cumulus, and cirrus have too strong a hold on 



Fig. 2.— Cumulo-nimbus (same cloud a^ in l-ig. 1 1. 



the vocabulary to be dislodged, and however much they 

 may be subdivided, they must remain the basis of classi- 

 fication. Mr. Ley therefore retains these terms, but an 

 eye educated by some fifty years of constant study, has 



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1315. VOL. 51 I 



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