recent progress in physics. 427 



§ 37. Influence of the thickness of the wire in the ther- 

 mometer. — The value of tlie constant n changes when another wire is 

 placed in the globe of the thermometer. Bless repeated the experiments 

 with wires of equal length, but of unequal thickness. Without 

 presenting the entire table containing the data of these experiments, 

 we shall consider only the final results. 



For wires of the diameter : 



0.119, 0.078, 0.0547, 0.05, 0.0225 lines he found for mean values 

 of n, 



0.18, 0.45, 0.88, 1.02, 2.69. 



From the equation — 



h = nt- 

 s 



it follows, that if experiments be made with the wires of equal length, 

 but unequal thickness, using the same battery (or like values of s) 

 with the same charge, (or constant value of q,) the depression h will 

 be as the value of n corresponding to this thickness of wire. Com- 

 paring the above values of n with the corresponding diameter of the 

 wire, we find that cceteris imribus, the value of n, and consequently 

 the depression of the column of liquid, or the heating of the air in 

 the globe of the air thermometer, is in proportion to the square of the 

 corresponding radii of the wires. 



Denoting the thickness of the above wires by 1, 2, 3, 4, and 5, the 

 squares of the radii of the 4th and 1st are as 0.05- to 0.119^, or as 

 0.0025 to 0.014169 ; but 



0.014169 _ .. 

 ^^0-2^ = ^•^^- 

 the corresponding values of n are inversely as the square of their 

 diameter ; for 



1.02 _ 

 008 = "-*"^ 



If we divide the square of the diameter of the wire 1 in the series 

 by the square of that of the other wires, the following quotients are 

 found : 



2.33, 4.73, 5.66, 28; 



but dividing the value of n for the first wire in succession into the 

 value of w for the 2d, 3d, &c., we get the following quotients : 



2.5, 4.88, 5.66, 15, 



which are very close to the above, excepting that in the case of the 

 finest wire the quotients 28 and 1.5 differ considerably. 



Disregarding this wire, it follows from the other experiments, that 

 the values of the factor ?i, and consequently the depressions in the air 

 thermometer, or the elevations of temperature of the air in the globe, 

 are inversely as the square of the diameter of the wires ; or in other 

 "words : The increase of temj^eraficre of the air in the globe is, cceteris 



