RECENT PROGRESS IN PHYSICS. 447 



in the second column correspond to what physicists are accustomed to 

 call the conductive capacity. 



§ 49. Capacity of metals for the development of heat. — When 

 a platinum wire 59.25 lines long, and 0.04098 lines in radius was in 

 the thermometer, and a copper wire 141.6 lines long, 0.041952 lines 

 radius, in the discharger a series of ohservations gave 



h = 1.51— . 

 s 



In these experiments a thermometer was used whose globe contained 

 22.668 ciihic lines, which in parts of the scale amounted to 188,404. 

 Hence a depression of 1 line, as shown in § 43 corresponds to a rise 

 of temperature of the air of 0°. 00802. The rise of temperature of! 

 the wire was found, as there shown, by the formula 



T = 0.00802 h 



V ^MCf 



(f 



The computation being performed we get, with — =: 1, for the rise 



of temperature in the platinum wire, 



0°.4635. 

 The wires being exchanged, so that the copper wire was in the 

 thermometer while the platinum was in the discharger, the result was 



;i=:0.46— ; 

 s 



and therefore, with - = 1, the rise of temperature of the copper 

 s 



wire is 



0°. 04678. 



Thus the same discharge produces in the two wires very unequal 

 temperatures. It is true that the thickness of the wires was not the 

 same, the radius of the platinum being 0.04098 lines, that of the 

 copper 0.04195 lines, but as shown above, the rise of temperature in 

 the wires being cceteris paribus as the fourth powers of the radii, a 

 platinum wire, therefore, with the same dimensions as the copper 

 wire, would give an increase of temperature of 



0.04098^ 

 0.4635 = 0°.4230. 



0.04195' 

 Thus the same discharge produces, in wires of platinum and copper 

 of like dimensions, increases of temperature which are to Ciich other 

 as 4230 to 0.04678 ; hence the same discharge produces in a copper 



0.04678 

 wire a rise of temperature ^ ^._^oq = 0.1106 times as great as m an 



equally thick platinum wire ; or copper has a capacity for the develop- 

 merit of heat 0.1106 times as great as platinum. 



