of Cumulus, Cirrus, and their Varieties. 365 



which is observed to take place at all angles with their polar- 

 isation. The direction of their motion and polarisation has, 

 however, a considerable influence on the coming weather. 

 When the two coincide in certain varieties of cirrus, the cha- 

 racter of the cloud remains unchanged during a considerable 

 time ; but, when they are at right angles to each other, the 

 fibres inosculate, and cirro-stratus results. It maybe remarked, 

 that all the varieties of cirro-stratus which are resolved into 

 cirro-cumulus possess polarisation ; and the same polarisa- 

 tion is observed after the resolution has taken place that was 

 noticed previously. This, with the entire change of the 

 masses of cirro-stratus into groups of cirro-cumulus, indicates, 

 I imagine, the existence of an agent acting in a manner 

 different from that mentioned by Mr. White ; namely, " the 

 excess of the ascending vapour over the evaporation." To 

 trace out this agent is, certainly, an interesting occupation for 

 meteorologists ; and it is to be hoped that more attention will 

 be paid, not only to the changes going on in the atmosphere 

 as measured by instruments, but, also, as indicated by clouds 

 and other meteors. Probably a series of careful electrical 

 observations, made with especial reference to such changes as 

 are above described, would be found of great utility. 



109. York Street, Whitechapel, June 1. 1836. 

 Te 9DfiIq naslisi 



P. S. I enclose a few extracts from my journal, which I 

 think calculated to elucidate the foregoing remarks. 



May 3. 1833. — It is very frequently noticed, that varieties 

 of cirro-stratus pass into cirro-cumulus. The latter modifi- 

 cation has three or four distinct modes of formation : it is 

 sometimes formed on a clear blue sky, as very minute roundish 

 masses ; at other times it is found to result immediately from 

 cirrus ; and, on some occasions, it is seen proceeding from 

 masses of cirro-stratus, until the latter modification is entirely 

 lost in the resulting cirro-cumuli. The cirro-stratus may be 

 divided into three groups ; namely, those that extend over 

 the whole atmosphere ; those that appear as bundles of fibres, 

 sometimes of very large dimensions, and at others very small, 

 the fibres in each case having a longitudinal arrangement; 

 and thosfe that appear similar to the smaller bundles, but, 

 with the fibres, instead of being arranged longitudinally, ar- 

 ranged transversely. It is the second group only, possessing 

 the longitudinal arrangement, that are resolved into cirro- 

 cumulus. When this takes place, it appears as if some 

 internal motion existed in the mass, by which the fibres were 

 destroyed and the small roundish masses produced. About 

 one p. m. of this day, numerous masses of this group of 



