154 YALE AGRICULTURAL LECTURES. 



England ; and when sheep husbandry shall have attained its 

 proper place, it will be found as a chief instrument in that result, 

 and their flocks will cover a thousand hills. 



Prof. B. SILLIMAN, JB.'S second lecture on Meteorology was 

 devoted to a description of the barometer, in its various forms, 

 and the practical rules derived from its observation, applicable 

 to the business of agriculture. 



He first illustrated experimentally the discovery of the ba 

 rometer, by Torricelli, in 1643. By means of an air-pump and 

 two barometers, one in and the other out of the vacuum, he 

 illustrated the influence of the atmospheric presence at the 

 height of the mercurial column. 



The model of the mercury barometer, made by Green, of New 

 York, after the directions of Prof. Guyot, of the Smithsonian 

 Institution, was exhibited, as well as other forms of this instru 

 ment. 



He alluded to the practical objections to the mercurial ba 

 rometer as an instrument for general use its cost, if well made, 

 and its unavoidable delicacy and fragility, which must always 

 act as a bar to its general use by the farmer. 



Fortunately we had, in the " aneroid " barometer, an instru 

 ment free from these objections. Sufficiently cheap, not liable 

 to be disordered easily, and withal sensitive and accurate 

 enough for the use which is made of the barometer as a 

 " weather prophet?" 1 He proceeded to give a popular descrip 

 tion of the essential features of the aneroid barometer (or ba 

 rometer " without a fluid," as the term implies). This instrument 

 was invented by Mr. Vidi, of Paris ; it is without mercury, and 

 consists of a flat and circular metallic box, the cover of which 

 is very thin and corrugated, or in ridges and furrows, concentric 

 with the walls. The air is exhausted from this box, which is 

 then hermetically sealed. The result is, that the elastic cover 

 rises and falls with every change in atmospheric pressure. By 

 means of a combination of levers and springs, these move- 



