Calometric Absolute Measurements. 



133 



cember, 1876, a resistance of 15*068 S. M. XL, or, reduced to 

 the temperature 16°, of 15*035 S. M. U. At the end of twelve 

 more experiments, in which a current of about 6 absolute 

 units passed through the wire each time during about 45 mi- 

 nutes, the latter showed, on the 28th March, at the tempera- 

 ture of 16°, the resistance 15*031 S. M. U. 



Accordingly, under the influence of continual currents of 

 absolute intensity from 4 to 6 the platinum wire underwent 

 no demonstrable alterations. A special investigation showed 

 that perceptible permanent alterations in the resistances of 

 metallic conductors only make their appearance from a definite 

 current-intensity onwards. 



Without further remarks, the following are the results of 

 the investigation. 



Here also I varied the experiments in several ways. First, 

 a series of twelve observations was instituted in which a pro- 

 portionally feeble current passed through the wire in the calo- 

 rimeter during a proportionally long period. From these 

 twelve observations the following values were obtained for the 

 mechanical equivalent of the unit of heat (the numbers are 

 based on the ordinary measure of work ; and with each is given 

 the external temperature £ a *to which the heat-unit on which the 

 result is based refers) : — 



ta. 



Date. 

 October 20, 1876 16*6 



» 21, 



» 26, 



» ^ 



„ 30, 



„ 31, 



November 5, 



» 6 > 



» "? 



» 15, 



» 16, 



» 20, 



16*7 

 16*3 

 18*1 

 18*5 

 18*0 

 16*2 

 16*0 

 16*4 

 17*1 

 18*0 

 19-1 



J. 



metre-kilograms. 

 428*49 

 428*12 

 425*51 

 426-93 

 429*93 

 429*56 

 428*18 

 427*28 

 426*95 

 428*50 

 426*46 

 427-19 



Hence the mean mechanical equivalent J of the heat-unit is 

 equal to 427*76 metre-kilograms (with a probable error of 

 ±0*23), if the specific heat of water at the mean temperature 

 employed, £ a = 17°-2, be put =1. 



A second series of twelve measurements was next instituted, 

 in which a proportionally stronger current was employed 

 during a shorter time. The results obtained in this series 



were :- 



