5.§ THE ISATUB^AL HISTORY OF CLOUDSr 



Nature of the Another conjecture might 3'tt be started ill to the cirrus, 

 ctrrus. Jt might be regarded as a cloud wholly formed of minute 



spiculae of ice; since the air, at a certain elevation, is suf- 

 ficiently cold thioughout the year for this effect. , Bpt if 

 it should be found, that the particles of cloutls are suscep- 

 tible of a rectilinear. arrangement in any case at a temper 

 ruture exceeding 32°, there would be no necessity fpr this., 

 supposition. 



If -the,, appearances of the cirrus are as frequq^t and va- 

 rious at sea as on land, it cannot be doubted, thatinteUigent 

 mariners vyonld find their account in keeping a register of 

 t^iem, as connected with the changes of wind, &j,'., inaHing 

 due aliowan'^e for the change of station in different observa- 

 tions when under sail. 



The bnoyapcy of thg cirrus seems- to be most perfect 

 during its first increase. It always follows, a^^ length, the 

 (^ommon course of gravity; and the change to the cirro- 

 cumulus, or cirro-stratus, which certainly depends on the 

 state of the medium it falls into, naay be ascribed to the X£i 

 teiUion or loss of ^he electricity. i^. 



^iin:bus. 



Of the Nature of the Nii;ihi{S. 



l?!tureof the This phenomenon may be thought to be improperly 

 denominated a modification of cloud, since it consists usually 

 of a column of descending rain, snpw, or hail, seen in con- 

 nection with the cloud affording it. As the concluding 

 [ink in the chain of atmospherical precipitation, it seems, 

 nevtirtheless, most advantageously placed here; and its his- 

 tory, though far from including all that we may observe, 

 and could wish to have explained, on the subject of rain, i^ 

 more decidedly illustrative of the nature of clouds ip general 

 than.tliat of any other modification. Moreover it is somcr 

 times observed to be formed before t4ie rain begins, whic^i 

 affords ^uf^t^i^^^nt ground fo<- considering it as a distinct 

 modificution of cloud. We owe to the bold and penetrat- 

 ing conjet^^ure of Franklin, on the identity of lightning 

 and the electric spark, the invention of a method of investi- 

 gating the electricity of clouds: which, in the hands of 

 experimentalists, has since brought out a mass of facts 

 ^biiadantlysulficient to establish tlat proposition; and which 



X alsc^ 



