Ii6 



THE NATURE BOOK 



rise and fall in large curves singing only 

 as they descend. 



The Wood Lark is silent usualh' after 

 mid-summer as are also Thrush, Black- 

 bird and Willow Wren, but the cessation 

 of song cannot be presumed upon as a 

 certain aid to identification, for it is a 

 constant accompaniment to nesting, and 

 if by any means the first attempt at 

 breeding comes to naught, the season 

 of song is then prolonged, and many 



birds that have been silent previously 

 for some weeks sing again with subdued 

 and shortened notes in early autumn. 



Early morning is the most likely time 

 for hearing the first spring notes of most 

 species, and it is then that the song is 

 generally most prolonged. At 4.50 a.m. 

 on April 26th, igoS, I counted the welcome 

 " Cuckoo " 8y times without intermission, 

 and at 6.45 a.m. on June 24th, 1885, 

 no fewer than 227 times ! 



Maurice C. H. Bird. 



HOW TO KNOW THE CLOUDS 



By WILLIAM J. S. LOCKYER, M.A., Ph.D., F.R.A.S. 



With Photographs by the Author 



III 



IF the reader will look back at the 

 cloud classification scheme he will 

 see that we have now arrived at the 

 heading " clouds of ascending currents," 

 and under it two forms of clouds are 

 mentioned — namely, cumulus and cumulo- 

 nimbus. The reason why these two 

 types are put in a class by themselves is 

 that they owe their origin to the daily 

 heating of the land by the sun, and the 

 consequent warming and rising up of the 

 air to higher levels. When this warm 

 moist air reaches altitudes in which it 

 can no longer maintain its moisture in 

 the invisible form, the vapour becomes 

 apparent in the form of a cumulus 

 cloud. On this account cumulus clouds 

 are m.ore common in summer than in 

 winter, and at midday more often 

 than in the early morning and late 

 evening. 



The reader will have no difficulty in 

 differentiating a cumulus type of cloud 

 from other types. Briefly, it may be 

 described as a thick cloud, the upper 

 portion of which is dome-shaped, or 

 sometimes, when the cloud is large, like 

 a cauliflower, and e.xhibits protuberances, 

 while its base is usually horizontal. 



" If woolly fleeces spread the Heavenly way, 

 Be sure no rain disturbs the summer day." 



The photograph on the opposite page 

 illustrates these small woolly cumuli, 

 which are often seen sailing along above 

 or past us during the summer months. 



This photograph was taken at Tun- 

 bridge \Xe\\s on May i8th, 1907, at 

 10.15 a.m., the camera being pointed 

 nearly due west. When such clouds pass 

 before the sun they appear very dark 

 with brilliant edges, and sometimes when 

 they are not too thick they present a 

 fine spectacle. 



It is on these occasions that one some- 

 times sees the very pretty effect of solar 

 beams being shot out from behind the 

 dark cloud. These shafts of light are, 

 of course, only the interspaces between 

 the shadows of the irregular portions of 

 the cloud which are cast on the air ; on 

 some days they are rendered far more 

 prominent than on others, but this may 

 probably depend on some particular con- 

 dition of the atmosphere. It is an old 

 idea that the ap})earance of these rays 

 indicates coming rain, as the following, 

 out of many old sayings, will show : 



"The sun is getting up his back stays, 

 And it is time to look out for bad weather." 



Perhaps, as the rays are only formed 

 when low clouds pass across the sun, 



