284 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY, 



would remark that this cloud-ring of the earth has a motion con- 

 trary to that of the axis of onr planet itself — that while the earth 

 was revolving rapidly from west to east, he would observe the 

 cloud-ring to go slowly, but only relatively, from east to west. 

 As the winds which bring this cloud-vapour to this region of 

 calms rise up with it, the earth is slipping from under them ; and 

 thus the cloud-ring, though really moving from west to east with 

 the earth, goes relatively slower than the earth, and would there- 

 fore appear to require a longer time to complete a revolution. 

 But, unlike the rings of Saturn through the telescope, the outer 

 surface, or the upper side to us, of this cloud-ring, would appear 

 exceedingly jagged, rough, and uneven. 



525. TJiunder. — The rays of the sun, playing upon this peak 

 and then upon that of the upper cloud-surface, melt away one set 

 of elevations and create another set of depressions. The whole 

 stratum is, it may be imagined, in the most turgid state ; it is in 

 continued throes when viewed from above ; the heat which is 

 liberated from below in the process of condensation, the currents 

 of warm air ascending from the earth, and of cool descending 

 from the sky — all, we may well conceive, tend to keep the upper 

 cloud-surface in a perpetual state of agitation, upheaval, and 

 depression. Imagine in such a cloud-stratum an electrical dis- 

 charge to take place ; the report, being caught up by the cloud- 

 ridges above, is passed from peak to peak, and repeated from 

 valley to valley, until the last echo dies away in the mutterings 

 of the distant thunder. How often do we hear the voice of the 

 loud thunder rumbling and rolling away above the cloud-surface, 

 like the echo of artillery discharged among the hills ! Hence 

 we perceive or infer that the clouds intercept the progress of 

 sound, as well as of light and heat, and that this upper surface is 

 often like Alpine regions, which echo back and I'oll along with 

 rumbling noise the mutterings of the distant thunder. 



52 G. Exceeding interest attached to physical 7-esearch at sea. — 

 It is by trains of reasoning like this that we are continually re- 

 minded of the interest which attaches to the observations which 

 the mariner is called on to make. There is no expression uttered 

 by nature which is unworthy of our most attentive consideration 

 —for no physical fact is too bald for study — and mariners, by 

 registering in their logs the kind of lightning, whether sheet, 

 forked, or streaked, and the kind of thunder, whether rolling, 

 muttering, or sharp, may be furnishing facts which will throw 



