MARCH OF THE THUNDER CLOUD. 225 



it between the two winds would bring it down in 

 rain, only that the opposing wind blows under it, 

 and the heat of that and of the earth repel it 

 upwards. The top projects the most, but both 

 that and the under side are turned back in a sort 

 of head, like that of a streamlet when it rolls 

 before it a stone which its force can barely roll, 

 and no more ; so that, long before it reaches the 

 zenith, there is a deep shade upon it, all but the 

 front edge, which, as it pushes on in curved scal- 

 lops, shows white sometimes on one, and sometimes 

 on another. When its edge is about the zenith, it 

 appears to move with greater velocity, as it is then 

 nearest to the eye. As it approaches the place of the 

 sun, the edge becomes very splendid ; and as there 

 are places which admit only the red rays of the 

 sun arid the heating rays to pass through, some of 

 the tints are dismal. The red light through the 

 thinner parts of the cloud, mingling with the re- 

 flected green from the earth, give the cloud and 

 the air under it a very smouldering and murky 

 appearance, as if the sky were about to be on fire. 

 If the cloud is to break where the observer is, the 

 lightning usually begins about that stage; the 

 first flashes being in the cloud, that is, through 

 the dry air that separates the different strata, and 

 the thunder is low and growling. But every flash 

 brings some of the strata together, and the col- 

 lected mass descends toward the earth with in- 

 creasing velocity ; but if the surface of the earth 

 is flat, the lower surface of the cloud also con- 

 tinues flat till it is near the earth ; and then its 

 approach is not without danger, as the longer that 

 the cloud holds together, the stroke is the more 

 violent ; but then, although more powerful, the 



