COHESION GF FtUIDS, g] 



4fo reign particles, the surface may even become conco.ve instead Application of 



of convex, and the depression be converted into an elevation. *f'*^' fioftnne to 

 ^ })n!(-i(ulaf 



But in barometers, constructed according to the usual fluids. 

 methods, the angle of tlie mercury M'ill be found to differ little 

 from l^O"; and in other experiments, M'hen proper precau- 

 tions are taken, the inclination will be nearly the same. The 

 <letermi nation of this angle is necessary for finding the appro- 

 priate rectangle for the curvature of the surface of mercury, 

 together with the observations of the quantity of depres5-ion in 

 tubes of a given diameter. The table published by Mr. Caven- 

 dish from the experiments of his father. Lord Charles Caven- 

 dish, appears to be best suited for this purpose. I have con- 

 structed a diagram, according to the principles already hiid 

 -dowa, for each case, and I find that the rectangle whiclj. 

 agrees best with the phenomena is .01. The mean depression 

 is always .015, divided by the diameter of the tube; and in 

 tubes less than half an inch in diameter, the curve is very 

 nearly elliptic, and the central depression in the tube of a 

 barometer may be found by deducting from the corresponding 

 mean depression the square root of one-thousandth part of its 

 diameter- There is reason to suspect a slight inaccuracy to- 

 wards the middle of Lord Charles Cavendish's Table, from q, 

 comparison with the calculated mean de])ression, as well as 

 from the results of the mechanical construction. The ellipsis 

 approaching nearest to the curve may be determined by the 

 solution of a biquadratic equation. 



li.imeter 

 inclies. 



Grains 'n 

 an inch. 

 C. 



Mean depres- 

 sion by cal- 

 culation. V. 



central depres- 

 sion by obser- 

 scrvation. C. 



Contral <3e- 

 prcssion by 

 lorm^la. Y. 



C^ntP»4 de- 

 pression by 

 diagram. Y. 



Marginal ; 

 pres^^ion 

 diagram. 



.6 



972 



.025 



.005 



(.001) 



.005 



.06(3 



.5 



675 



.030 



.007 



.008 



.007 



.067 



.4 



432 



.037 



.015 



.017 



.012 



•<i69 



.35 



331 



.043 



.025 



.024 



.017 



.072 



.30 



243 



.050 



.036 



.033 



.027 



.079 



.25 



169 



.060 



.050 



.044 



.038 



.086 



.'20 



108 



.075 



.067 



.061 



.056 



.096 



.15 



61 



.100 



.092 



.058 



.085 



.116 



.10 



27 



.150 



.140 



.140 



.140 



,161 



The square root of the rectangle .01, or .1, is the ordinate 

 where the curve would become vertical if it were continued ; 

 but in order to find the height at which it adheres to a vertical 



Vol. XIV.— May, ISO^. M surface, 



