Mr. W. S. Jevons on the Forms of Clouds. 247 



rough calculation which I have made leads to the conclusion 

 that the effect of the latent heat considerably overbalances that 

 of the heavy watery particles ; but from the difficulty of obtain- 

 ing satisfactory data as to latent and specific heats, I cannot 

 here pretend to determine the point. It is sufficient if the fol- 

 lowing be distinctly understood and allowed*: — 



1st, That in the formation of a cumulose cloud, some came 

 exists to check the rising column of air, and sooner or later to 

 cause it to descend below the plane of precipitation. 



2nd. That the weight of the precipitated watery particles must 

 contribute in some degree to produce this effect. 



Cumulost'atus. 



17. The cumulostratus, which I have seen aptly described as 

 the anvil-shaped cloud, possesses a peculiar and distinctive form. 

 It is a cumulus of which the higher jjarts or the summit extend 

 horizontally into stratose projections, and is said to be the inter- 

 mediate or transition form between the cumulus and the nimbus 

 or storm-cloud. 



18. The following are the conditions under which it was found 

 that a miniature cloud, bearing a striking resemblance to the 

 natural cumulostratus, could be produced in the section-glass 

 (see figs. 3 and 4). 



Exp. 2. Place in the section-glass a stratum of water con- 

 taining only a trace of common salt, and then gradually intro- 

 duce below it a second stratum containing the same trace of com- 

 mon salt, together with 2 parts in 1000 of sugar. The latter 

 stratum, possessing the greatest specific gravity, will lie tran- 

 quilly below the first. Lastly, project up slowly from the lower 

 side of the apparatus, a jet of water containing a trace of nitrate 

 of silver, together with about 1 part in 1000 of sugar. 



19. The last-mentioned liquid is of a specific gravity inter- 

 mediate to the other two, and will ascend through the lower stra- 

 tum and up to a certain elevation in the higher stratum. There 

 its superior gravity will overcome its momentum, and it will 



* The following pliseuomenon w liicli I uotieed a few days since, presents 

 such a rare and remarkable coufirniation of what is advanced above, that I 

 describe it liere : — During a severe hot wind (December 24, 1857, tempe- 

 rature of air 104° to 108° F.), a large column of smoke (probably from a 

 bush fire) was seen rising into the atmos])here in the neighbourhood of 

 Sydney. After attaining a certain elevation, this was sharply terminated 

 by a nearly level plane, beneath which the smoke seemed to spread out on 

 all sides. Uut in several places small cumuli projected up above this plane, 

 remaining in contact \vith it and a])pcaring as if supported upon it. Here 

 we have, in all ])robabihty, the j)lane of ))rccii)itati<)n distinctly marked, 

 and a ])roof that the ascending column of air- could not permanently rise 

 above it. 



