142 Mr. T. Hopkins on the Formation of the Cumulus Cloud. 



densation of steam taking place in the atmosphere there will 

 be an upward atmospheric movement, which will cause fresh 

 condensation and further upward movement, and this process 

 may form the cumulus cloud, which may rise to a less or greater 

 height in the atmosphere, and the cloud may be dissipated or 

 may give out rain according to the quantity of steam contained 

 in the atmosphere, and the condensing power of cold. 



The atmospheric movements which have been here consi- 

 dered, are represented by Mr. Espy as originating with, and 

 caused by, the direct heating power of the sun, but the action 

 of the sun may be only one of the causes which produce the 

 phenomena. Any cause which shall have the effect of ele- 

 vating a column of the atmosphere sufficiently to cause con- 

 densation of steam to begin, may commence the process de- 

 scribed, and cause cumuli to form. A current of air having 

 nearly a maximum quantity of steam for the temperature, be- 

 ing forced by the inertia of the mass against a ridge of hills, 

 the lower part must rise, and in rising must force up the whole 

 of the column that rests upon it. This forcing up may be 

 sufficient to raise the column high enough to condense some 

 of the steam which it contains, when all the effects just de- 

 scribed would take place in the same way as would have 

 occurred, if the heating power of the sun, acting on the sur- 

 face of the earth, had been the prime mover. In this way the 

 ridges of mountains in Caernarvonshire and Merionethshire 

 may force up the current of air flowing against them from 

 the south-west, until the process of condensation commences 

 and clouds are formed. And the long lines of cumuli flow- 

 ing apparently from about Snowdon northward towards 

 Westmoreland, or eastward towards Yorkshire, when they 

 reach the English hills may get another lift, and the co- 

 pious rains that fall in those parts may be thus accounted 

 for. If mountains can force up atmospheric currents, it is 

 evident that when different atmospheric currents move ir- 

 regularly, one may force up another. On two currents 

 meeting or crossing each other, one may force its way under 

 the other, lift it up, and thus cause condensation to com- 

 mence. In this way cumuli may be formed over land or sea, 

 and rain may be discharged, and possibly even storms com- 

 menced, provided there be an adequate supply of steam for 

 condensation ; and all this may take place in the absence 

 of the sun, — in the night as well as in the day. Should va- 

 rious currents moving in opposite directions penetrate each 

 other at different elevations, it will follow, from what has been 

 advanced, that clouds may be formed at the same time at dif- 

 ferent elevations, and each stratum of cloud may be affected 



