HOW TO KNOW THE CLOUDS 



119 



sions to which cumulus clouds attain, 

 but he must remember that the cloud 

 in question was a great distance off. 

 This cloud had the appearance of being 

 of the cumulo-nimbus type, although one 



base of a cumulo-nimbus may be about 

 4,700 feet from the ground, its apex or 

 top may extend to an altitude of about 

 26,000 feet ; the vertical thickness of 

 such a cloud measures then approximately 



CUMULO-NIMBUS CLOUD. 

 Photographed at a great distance, and is therefore of very large dimensions. 



could not be certain, as it did not pass 

 overhead. 



It was possibly in the initial stage 

 of becoming a thunder cloud, although 

 it had not then begun to flatten out at 

 the top and assume the anvil form, the 

 general feature of thunder clouds. The 

 photograph from which this reproducticjn 

 has been made was taken at South Ken- 

 sington in 1906 on May 25 at 9.30 in the 

 morning. 



The great heights to which thunder 

 clouds can attain may be gathered from 

 the fact that they sometimes reach the 

 level of the upper clouds, the average 

 heights of which are about 29.500 feet. 

 M^iasurements have shown that while the 



21.500 feet. When we remember that 

 Mount Everest, the highest mountain in 

 the world, rises 29,000 feet from sea level, 

 some idea of the magnitude of these 

 clouds may be grasped. 



It sometimes happens that the under 

 surface of a cumulo-nimbus presents a 

 mammillated ajjpearance — that is, droops 

 dfjwnwards, like a festoon of drapery. 

 When this is the case it is termed mam- 

 mato- or festooned-cuniiilus. This pecu- 

 liar feature does not seem to be of common 

 occurrence in this country, and I have 

 only noticed it on two occasions. For- 

 tunately, on one of these, May 21st, iqoG, 

 at 1.30 p.m., the camera was available, 

 but the feature was somewhat less pro- 



