Makch 9, 1922] 



NATURE 



301 



stage forward on its journey towards the ever-unattain- 

 able goal of perfect knowledge. It is still the history 

 of the individual written from the behaviour of the 

 crowd. Some day another Abegg will tell the story 

 of the next stage, perhaps the history of the crowd 

 written from the behaviour of the individual. However 

 that may be, we chemists of the present generation 

 cannot be too grateful to Abegg for the work which 

 he did in bringing inorganic chemistry abreast of the 

 progress of chemical science. 



F. G. DONNAN. 



Cloud-Forms. 



Le Nubi. By L. Taffara. Parte i, Testo. Pp. 67. 



Parte 2, Atlante. Tav. 26. (R. Ufficio Centrale 



di Meteorologia e Geodinamica Roma.) (Roma : 

 Tipografia Ditta L. Cecchini, 1917.) 



THE recent revival of interest in cloud -forms 

 which has expressed itself in the publication 

 of various collections of photographs is well illustrated 

 by the atlas which was prepared by Signor L. Taffara 

 and issued in 191 7 by the Meteorological Institute 

 of Rome, together with an introductory text which 

 is reprinted from vol. 37 of the Annali of the 

 institute. 



The text leads up to a chapter on procedure in 

 the observation of the height and motion of clouds. 

 On the way it explains the history of the study of 

 clouds on the basis of international agreement, the 

 original specification of ten cloud types, the inter- 

 national atlas of 1895, t^^6 revision at the International 

 Conference at Innsbruck in 1905 and the republication 

 of the atlas in 1910, which included the ten types and 

 nine variants with a special note on clouds of a type 

 called " lenticularis," the importance of which be- 

 comes increasingly evident. In the meantime (1907) 

 the late M. Vincent, of the observatory at Uccle, 

 Brussels, had published an atlas of cloud-forms with 

 much more elaborate classification, which had been 

 followed by Dr. Loisel, of the observatory of Juvisy 

 (Paris), in 191 1. The suggested classification includes 

 nine species, comprising twenty-one varieties of lower 

 cloud ; two species, twelve varieties of middle cloud 

 (which may further require one of the adjectives 

 " undulatus," " striatus," or " mammatus ") ; and 

 four species, nineteen varieties of high cloud, which 

 may require further discrimination as " undulatus," 

 altogether fifty-two forms of cloud to be discriminated, 

 or upwards of one hundred if discrimination by ad- 

 jectives is included. Of the many additional variants 

 that are thus introduced, two — namely, pallio-nimbus, 

 which seems to be a good formula for a rainy day, 

 NO. 2732, VOL. 109] 



and alto-cumulus castellatus, a sign of approaching 

 thunder — seem to have acquired merit. Signor Taffara 

 accepts this classification as being the most complete, 

 and in his atlas gives forty-nine photographs (includ- 

 ing three autochromes), most of them by himself, 

 but some by Mascari, Loisel, Gamba, Ponte, Peret, 

 Neuhaus, a pastel by Scalla, and two water-colour 

 drawings, which illustrate thirty-six of the hundred 

 examples, and one more type in addition, which is 

 defined as " lenticularis." It does not occur in the 

 list quoted from Vincent. The reproduction of the 

 photographs is excellent ; the art of photography of 

 clouds is the subject of a special chapter of the text. 

 The collection forms a beautiful book. 



Among the pictures are two very definite types of 

 cloud which belong to the region of Mount Etna and 

 are admirably represented by reproductions of Signor 

 A. Marcari's photographs ; these are " la serpe," a 

 long serpentine cloud shown straggling along like a 

 snake, low on the mountain ; and " Contessa del 

 vento," a stationary cloud of the Valle del Bove, 

 of which no fewer than five examples are given. These 

 clouds are disposed of in the classification as being 

 " cumulus humilis," in association with othei: cumulus 

 of low level ; but the obviously lenticular nature of 

 the " Contessa del vento " marks it out as being 

 something entirely different from any of the hundred 

 forms. It looks like a gigantic white turban, the 

 crown of which merges into other clouds, and it 

 suggests the core of an eddy, possibly formed mechanic- 

 ally by the mountain, since all lenticular clouds seem 

 to be associated with peculiar dynamical conditions 

 due to the unevenness of the surface. If the lenticular 

 shape indicates the locus of formation of cloud in 

 wind that blows through the cloud, not with it, as 

 it appears to do in other cases, we have apparently 

 in these clouds an opportunity for studying the con- 

 ditions at close quarters. 



We are scarcely yet in a position to make a final 

 classification of clouds, and the elaborate classifica- 

 tion into some hundred forms is somewhat premature. 

 Presumably we should begin by drawing a dis- 

 tinction between individual clouds and cloud-groups. 

 Cumulus is a cloud, alto-cumulus a cloud-group. It 

 is questionable whether a vast layer which discloses 

 small cumulus on its margins is fairly classified by the 

 appearance of the cloudlets there. We have no 

 sufficient principles of classification, and for that 

 reason a multitude of discriminatory characteristics 

 scarcely helps us at this stage. The contribution to 

 our knowledge of different forms which the Ufficio 

 Reale has made through the agency of Prof. Taffara 

 is a valuable addition to the material from which 

 classification will at some time emerge. It seems 



