Equatorial Cloud-Rings of the Earth. 93 



surprised to find that, notwithstanding the oppressive weather of the 

 rainy latitudes, both his barometer and thermometer stood lower in 

 them than in the clear weather on either side of them. In pass- 

 ing that rainy latitude, he has passed a cloud-ring which encircles 

 the earth. 



Lieutenant Maury then proceeds to give a description of the va- 

 rious changes which this great equatorial cloud-ring undergoes, and 

 of its effects on the climate over which it hangs, the laws which con- 

 trol its shifting, sometimes to the north and sometimes to the south 

 of the equator, and the accessions it receives from the more tem- 

 perate latitudes, while the ring itself is the great source of supply 

 of moisture to the regions of the earth very distant from the 

 equator. Thus this cloud-ring modifies the climate of all places 

 beneath it ; overshadowing at different seasons all parallels from 

 5° south to 15° north. It may be asked, where do the va- 

 pours come from which are condensed and poured into the sea as 

 rain ? They come from the trade-wind regions under the cloud- 

 ring, then rise up, and as they rise they expand, and as they expand 

 they grow^cool and are condensed. There is, therefore, a ceaseless 

 precipitation going on under the cloud-ring. Evaporation under it 

 is suspended nearly the whole year round. This ring is formed by 

 the meeting of the NE. and SE. trade-winds ; the vapours which 

 each bring from northern and southern regions meet and ascend. 

 Our knowledge of the laws of nature will tell us, therefore, that the 

 atmosphere will be cooler under this ring than on either side of it, 

 without consulting the thermometer. Were the clouds which over- 

 hang this belt luminous, and could they be seen by an observer from 

 one of the planets, these clouds would present an appearance not un- 

 like the rings of Saturn. He would also observe that this ring had 

 an apparent movement contrary to that of the earth ; for though it 

 moves with the earth, the motion of the ring is relatively slower, and 

 the earth slips from under it, giving the ring an apparent slow mo- 

 tion from east to west. This ring would be unlike those of Saturn 

 in another respect : its edges would appear very jagged, and rough, 

 and uneven. 



Navigators are now learning to tell by the barometer when they 

 have passed the cloud-ring. In the log-book of an American Captain 

 in a voyage round the world, in 1850-51, recently forwarded to the 

 National Observatory, I find the following remarks : — " I here pre-' 

 diet," he says, before reaching the equator, " the barometer will re- 

 main below 30 in, until we get without the influence of the rainy 

 latitudes." After having crossed a belt of five or six degrees of lati- 

 tude, within which such remarks are frequent, as " Warm and sul- 

 try ;" " Heavy rains ;" " Very murky and close at times ;" " Quite 

 oppressive,'' "Rain," &c ; — on the seventh day he remarks, " As- 

 suming the settled weather of the trades, only requiring a rise of 

 barometer to assure me of that fact." The day after, I find in his 



