THE 



PHILOSOPHICAL MAGAZINE. 



I. On file Modifications of Clouds, and on (he Principles 

 of their Production, Suspension, and Destruction ; being 

 the Substance of an Essay read before the Askesian Society 

 in the Session 1802-3. Bi/ Luke Howard, Esq. 



[Continued froin vol. xvi. p. 357.] 



1 



Of the Formation of the Cirrus. 



T must have been owing entirely to the want of distinc- 

 tive characters for clouds, and the consequent neglect of 

 observing their changes, that the nature of this modification 

 more especially has not engaged the attention of electri- 

 cians. The attraction of aggregation operating on solid par- 

 ticles diffused in fluids does indeed produce a great variety 

 of ramifications in the process of crystallization : but these 

 are either uniform in each substance, or have a limited 

 number of changes ; and in no instance do we see the same 

 substance separaung from the same mediutn, and, uncon- 

 fined in its movements, rival the numerous metamorphoses 

 of the cirrus. 



The great elevation of these clouds in their ordinary mode 

 of appearance has been ascertained both by geometrical ob- 

 servations* and by vicv/ing thein from the summits of the 

 highest mountains, when they appear as if seen from the 

 plain. A more easy and not less convincing proof may be 

 had bv noting the time during which they continue to re- 

 flect the different coloured rays after sunset, which they do 

 incomparably longer than any others. The same configura- 

 tion of cirrus has'been observed in the same quarter of the 

 ^ky for two successive days, during which a smart breeze 

 from the opposite quarter prevailed below. 



Jt is therefore probable that this modification collects its 

 water in a comparatively calm region, which is sometimes 

 incumbent on the current next the earth, and almost out of 

 the reach of its daili/ variations in temperature and quantity 



* " The small white sire^ks of condensed vapour which appear on 

 tlie face of tlie sky in scitne weather 1 li:ive, by several careful obser- 

 Vdtions, found to be from three to five miles above the earth's surface." 



\ olT.XVII. No. 05. A 3 of 



October 1SU3. 



