lO 



THE NATURE BOOK 



most important feature of the scene — 

 namely, colour. 



The day, however, is not far distant 

 when, owing to the researches of a long 

 list of ardent workers, true colour photo- 

 graphy will be an accomplished fact. 

 Then, and then only, shall we be able to 

 depict faithfully and instantaneously both 

 the forms and colours of the sky and 

 clouds. Each of us will be able to secure 

 and cherish our own gems in the nature 

 of brilliant red sunsets or golden dawn 

 effects. 



To return, however, to the utilitarian 

 side of the subject, it is proposed here 

 to consider only the question of the ap- 

 pearances of the different kmds of clouds, 

 and so help the reader that he may be 

 able to recognise and correctly name 

 them himself, preparatory to comparing 

 their appearance with the actual or sub- 

 sequent weather conditions experienced. 



Perhaps it is hardly necessary to state 

 that numerous classifications of cloud 

 forms have been suggested from time to 

 time by those who have gone deeply into 

 the subject. As far back as the year 

 1803, Luke Howard was one of the first 

 who brought out a system of nomenclature 

 — and this was so good that it held 

 first place up to quite recent years. 

 Many other attempts at a more scientific 

 classification have also since that date 

 been made, but the majority of them, 

 with perhaps the exception of that of 

 Clement Ley, were simply makeshifts. 



The reader will quite understand how 

 important it is to have one classification, 

 because, with many current, the same 

 type of cloud could be, and was, called 

 by several different names. It was hope- 

 less, then, to discuss from a scientific 

 point of view the observations of several 

 workers, since the nomenclature in many 

 cases was so different. 



The question was, however, settled l)y 

 the International Meteorological Com- 

 mittee, which specially appointed a sub- 

 committee to report on the various 

 classifications in use, and to devise a 

 more simple and efficient system. The 

 result of this step was that an international 

 system of cloud nomenclature was agreed 

 to by the heads of all the meteorological 

 institutions throughout the world. Not 

 only this, but an international cloud 



atlas, with text in English, French, and 

 German, was soon published, and is 

 now in general use wherever scientific 

 observations of clouds are made. 



Before stating the details of this classi- 

 fication, it is as well to become familiar 

 with three conspicuous forms of cloud- 

 structure which are quite distinct in appear- 

 ance. Perhaps the most common form 

 of them all is that which has a heaped- 

 up appearance, lumpy, in fact, with the 

 under surface more or less horizontal. 

 This form of cloud is sometimes very 

 striking by reason of the great thickness 

 in its vertical direction, and it occasion- 

 ally puts on the ap])earance of an enor- 

 mous cauliflower. This form of cloud is 

 tenned cuinidiis. 



In great contrast to this, we have a 

 form of cloud which arranges itself in 

 long, horizontal sheets or layers. In 

 this case the vertical height is insignificant 

 compared to its great extension in the 

 horizontal direction. The name given to 

 this shape is stratus. 



The third and last prominent form is 

 that which presents a hairy or fibrous 

 appearance. It is usually very delicate 

 in structure, and sometimes takes the 

 form of feathers stretching across the 

 sky, occurs only at high altitudes, and 

 is known as cirrus. 



When the reader has well mastered these 

 three main varieties of cloud, he has a 

 firm basis on which to class the other 

 manifold characters which the clouds at 

 times assume, since they are all simply 

 stages of gradation between those types. 



It must not be forgotten, however, that 

 clouds are formed at nearly all altitudes. 

 Sometimes they are actually on the 

 ground, when they are called mists or 

 fogs. Sometimes, again, in mountainous 

 districts they are seen to enwrap for a 

 time the mountain peaks. We observe 

 such clouds in the illustration on 

 page 9, which, as they passed the 

 mountain toj:) from which this view was 

 taken, envclo})ed it in a thick mist for 

 the time being. The mountain in ques- 

 tion was the Esel, one of the peaks of 

 Mount Pilatus, near Lucerne. This peak 

 rises 6,962 feet above sea level, and the 

 small bundles of cloud visible near the 

 middle of the picture are just about to 

 obliterate the view of the town of Lucerne, 



