388 ANNUAL OF SCIENTIFIC DISCOVERY. 



Sailors have opportunities of making observations on clouds, and the 

 various phenomena accompanying them, which no other class enjoy. 

 The sailor, bound in his ship to the southern hemisphere, enters the 

 region of the north-east trade winds, and frequently finds the sky mot- 

 tled with clouds, but generally clear ; continuing his course south, he 

 observes his thermometer to rise as he approaches the equator, until, 

 entering the equatorial region, he finds the weather to become murky, 

 close and oppressive. He then enters the south-east trades ; and, on 

 looking at his log-book, he is 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 passing that rainy latitude, he has passed a cloud ring 

 which encircles the earth. 



Lieut. Maury then proceeds to give a description of the various 

 changes which this great equatorial cloud ring undergoes, and of its 

 effects on the climate over which it hangs, the laws which control its 

 shifting, sometimes to the north and sometimes to the south of the 

 equator, and the accessions it receives from the more temperate lati- 

 tudes, while the ring itself is the great source of supply of moisture to 

 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 five degrees south to fifteen degrees 

 north. It may be asked, where do the vapors 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 N. E. and S. E. trade winds ; the 

 vapors 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 overhang 

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

 the planets, these clouds would present an appearance not unlike the 

 rings of Saturn. He would also observe that this ring had an appar- 

 ent 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 motion 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- 

 dict," he says, before reaching the equator, " the barometer will 

 remain 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 sultry ;" 

 " heavy rains ;" " very murky and close at times ;" " quite oppres- 



