68 



THE NATURE BOOK 



1 



MMIiLS CLOLlJ. 

 Photographed at Tunbridge Wells, May 18, 1907, at 11.33 a.m. 



better than any photograph would do. 

 It consists simply of a thick sheet of a 

 grey or bluish colour, and in the neigh- 

 bourhood of the sun or moon shows a 

 brilliant patch. Unlike cirro-stratus, it 

 does not give rise to halos, but sometimes 

 causes coronae (bright rings, closely sur- 

 rounding the sun or moon). Measure- 

 ments have shown that this type of cloud 

 is only half as high as the cirro-stratus 

 type- 

 Passing now to the lower clouds, we 

 come to the straio-citiniiliis, a cloud which 

 is too irregular to be called stratus and 

 not sufficiently lumpy to be called a 

 cumulus. This type signifies large, globu- 

 lar masses or rolls of dark cloud, which 

 frequently cover the whole sky, especially 

 in winter, and sometimes presents a wavy 

 appearance. The masses are not dense, 

 and between them l)lue sky is often seen. 

 In fact, we have here a type of cloud 

 which is very much like the alto-cumulus, 



only situated at a much lower level, and 

 consequently the cloud masses appear 

 on a rather larger scale. The lower 

 illustration on page 67 will serve to illus- 

 trate this type. The original photo- 

 graph was taken at Tunbridge Wells, 

 on December 25th, 1906, at 11 o'clock. 

 The brightest part of the picture in the 

 lower })ortion indicates the neighbour- 

 hood of the winter sun, which was 

 obscured most of the morning by this and 

 by alto-cumulus form of cloud. 



We now come to the nimbus, or rain 

 cloud. This tvpe is composed of a thick 

 layer of dark clouds without any definite 

 shape, and with ragged edges, from which 

 rain or snow generally falls. Its apj)roach 

 is usually accompanied by a great diminu- 

 tion in daylight, and in consequence is 

 not an easy object for the camera. Under- 

 neath the layer of nimbus there are, as 

 a rule, small loose clouds which may 

 have become detached from the main 



