THE ilATURAL HISTORY OF CLOUD^. SS 



iii clanger of admitting a greater number than are really ne- Nature of the 

 cessary. It is apparent, however, that in the state^f ihina? cumulo stra- 

 niost favourable to the production of the cumulo-stratus, 

 there exists a precipitation, independent of that which gives 

 ris^e to the cumulus, and situate in a higher region. Afi 

 this precipitation affoids sometimes the cirro-cuaiuluS, at 

 qihers the cirro-stratus, we need nqt assign to it any other 

 cause than the one iai ready mentioned, vi?. a superior vapor- 

 ized current of air. It is not inconsistent with the princi- 

 ples we have laid down respecting the cumulus, that this 

 cloud should ialso be produced at the same time; it being 

 requisite on\y that there exist a sufficient action of the sun 

 on the Earth's surface, or a sufficient tenij>erature derived 

 therefrom. Tiie inosculation of these two orders of cloud, 

 the singailar unior| wjiich follows, and the e^tab^!4lmen| of a 

 new centre of attraction, towards which the whole future 

 increase tends, is the prominent feature in this modification, 

 and the chief fact which remains to be accounted for. As 

 this effect is not constant and uniform, it cannot be ascribed 

 to gravity alone. Reasoning from analogy, rather than from 

 direct experiment, vviiich it is not easy here to apply, we may- 

 attribute it to a difference in the electric charge pf the re- 

 spective clouds; which difference, though ?njall, onjjht to 

 produce the usual appearances of bodies charged plus and 

 ininus; viz. mutqal approach and contact. This effect, 

 howevei:^ appears to ensue rather with regard to the masses 

 than to tlie individual particles. 



The effect of the highly vaporized stat* of the higher at- 

 mosphere is often discernible in the cuniulusfrom its earliest 

 appearance; and it is easy to determine, #t certain ti-nes, 

 that this cloud, if it continue long, will pass to the piesent 

 modification. The effect we inean tq point out is the un- 

 y«yen growth of the cloud ; numerous small masses attaching 

 themselves to its surface, SRid giving it an appearance not 

 unlike the curls of a fleeqe of wo6l ; particularly when seen 

 beneath the sun, in a situation where the projecting parts 

 may catch the light. If we admit that^he cumulus acts* 

 ms well by electrical attraction, as by that of gravity, on the 

 surrounding materials, yit niay here consider them as arriv- 



