May 19, 192 1] 



NATURE 



365 



Cloud Forms.^ 

 By Capt. C. J. P. Cave. 



A/TOST writers on clouds put forward their 



J-' A own system of classification, much to the 



confusion of the subject; Mr. G. A. Clarke is 



Fig. I. — Lenticular cirro-cumulus at sunset. From "Clouds." 



cumulus, some giving details of structure, 

 and some whole skyscapes of these the most 

 beautiful of all the forms of clouds. Very 

 noticeable is the plate of cirro- 

 stratus, " a thin whitish sheet ot 

 clouds," and therefore very 

 difficult to depict satisfactorily. 

 Mr. Clarke has carefully studied 

 lenticular clouds and gives many 

 examples, while in the text will 

 be found a discussion of these 

 extremely interesting and hither- 

 to rather neglected forms of 

 cloud ; an example, perhaps the 

 most striking photograph in the 

 book, shows such a cloud with 

 its front edge lit up by the setting 

 sun, while part of its under 

 surface, also in sunshine, is 

 broken up by a double set of 

 ripple marks (Fig. i). There is 

 no doubt that the cloud sheets 

 have been rendered by Mr. 

 Clarke better than has been done 

 in any previous publication ; but 

 some of the photographs of 

 cumulus leave something to be 

 desired, chiefly owing to the use 

 of a lens cf too narrow an angle 

 therefore to be congratulated on adhering to the I for the size of the clouds ; pictures of cumulus 

 international classification in his recently pub- gain in effect if the main cloud does not fill up 

 lished book. He says that even to divide the { the whole of the picture.. The most remarkable 

 recognised types into sub-types 

 makes the classification unwieldy, 

 and is open to the objection that, 

 " particularly in the case of the 

 cirrus . . . one sub-type may be 

 transformed into another and 

 then perhaps return to its origi- 

 nal form all within the space of 

 a few minutes." He even sug- 

 gests that any change should 

 rather be in the direction of 

 further simplification. In chap. ii. 

 the international classification is 

 given in full, so that for English 

 readers Mr. Clarke's book may 

 well supersede the Cloud Atlas, 

 for the former contains all the 

 essentials to be found in the text 

 of the latter, and the illustrations 

 cannot for a moment be com- 

 pared. Where the atlas gives a 

 few illustrations, some very indif- 

 ferent, of each type, Mr. Clarke 

 gives numerous examples that 

 for variety, wealth of detail, and 

 excellence of production easily 

 surpass previous pictures. 



There are many plates of cirrus and cirro- 



(I.ondon : 



1 "Clouds." By G. A. Clarke. Pp. xvi + i36-f40 plates. 

 Constable and Co., Ltd., 1920.) au. net. 



NO. 2690, VOL. 107] 



Fig. 2. — Rainbow on screen of rain falling in middle distance. From " Clouds." 



plate in the whole book from a photographer's 

 point of view is that which shows a rainbow on 

 the shower from the base of a cumulo-nimbus 

 cloud (Fig. 2) ; to show a rainbow, three super- 



