of the Genus Condylura, 



583 



hand eight tenths of an inch. Length of the longest nail three 

 tenths of an inch. Length of the foot one inch and one tenth. 

 Length of the longest nail of the foot five twentieths of an 

 inch. Distance between the eyes rather over three tenths 

 of an inch. From the end of the snout to the eyes seven 

 tenths of an inch. 



Milton, May 4, 1825. 



Art. LXI V. — On the Application of the Barometer to the Mea- 

 surement of Heightsl* 



In the barometer there is an equilibrium between the pres- 

 sure of the mercury and that of the atmosphere. Now when 

 two fluids thus counterbalance each other, the altitudes are 

 inversely as the specific gravities. Accordingly, as the spe- 

 cific gravity of mercury is to that of air at the surface of the 

 earth as 13,57 to 0,00122, we shall have 



0,00122 : 13,57 : : 30 : ' ^ = 333688. 

 ' ' 0,00122 



We infer, therefore, that the height of the atmosphere, on the 

 supposition of a uniform density throughout, is 333688 inches, 

 or a little more than 5 miles. But the air being eminently 

 elastic, the lower strata are compressed by the incumbent 

 weight of those above, so that the density becomes less and 

 less continually as we ascend. Let the weight of the column 

 of mercury which measures the pressure of the atmosphere, 

 exerted upon a unit of surface, be denoted by g A /i, g being 

 the force of gravity, A the density of the mercury, and h the 

 perpendicular height of the column above the level of the 

 surface in the basin, and let the weight of the atmosphere 

 lapon the same surface be denoted by w, we shall have 



g A h = w. 



As we ascend into the atmosphere, the weight w and the 

 height h diminish continually, and these diminutions depend 



* This article is, with the permission of Prof. Farrar, taken from " An 

 Elementary Treatise on Mechanics, comprehending the Doctrine of Equili- 

 brium and Motion, as applied to Solids and Fluids, compiled from the most 

 approved writers, and designed for the use of the Students of the University 

 at Cambridge, N. E." Not yet published. 



