OF ARTS AND SCIENCES. 493 



being raised, a sufficient extra resistance was inserted in c, so that 

 when A'2 was momentarily depressed, and A'^ was immediately after- 

 wards again depressed, the spot G^ did not move. The hand soon 

 became accustomed to pressing K^ just long enough to accomplish this 

 result. In the experiments, c had to be increased from 1,167 ohms by 

 the amount of 50 ohms, and the temperature of the strip accordingly 

 rose about ten degrees. As the resistance was measured almost simul- 

 taneously with the passage of the current, the rise in temperature 

 could be very exactly known, and the effect of radiation could be very 

 easily determined. 



Combining equations (1) and (2), we have 



j^ EHT^ (r+S) «/3 ^ 



Gtt S ws (/i\ — Bq) ' 



E, as measured by the electrometer, was about one volt, = 10^ C. G. S. 

 units. H was .171 ; r, the resistance of the ballistic galvanometer, 

 was 3,296 ohms ; S^, the shunt, was 1,025 ohms; T', the time of a 

 single vibration of the needle, was 12.6 sec; a, the resistance of the 

 strip at 0°, was 1.072 ohms; ;3 was .00503, the weight of the strip 

 was .230 gr. ; its specific heat, .114; the gain in resistance of the 

 strip was .05 ohm, and 5, from twenty experiments, was 26.8 cm. 

 G was 769.4 for S= 1. 



,_ IQs X -171 X 12.6 X 26.8 X 4.321 X 107-2 X -00503 

 "~ 7G9.-1 TV .05 X 1-02.3 X -230 X -114 



= 4.14 X 10^ ergs per gram-degree. 



In Joule's experiments, the process of heating was continued for 

 nearly an hour, whereas here it lasts for less than a second. In the 

 former method, it was necessary that the current should remain sen- 

 sibly constant throughout the experiment, and the calorimeter wa8 

 radiating heat throughout that time. In the short time required by 

 the latter method, the radiation must be very small, and the error from 

 the inconstancy of the current is avoided. I intend to undertake a 

 further course of experiments in order to obtain an accurate determi- 

 nation, the purpose of the present paper being merely to show the 

 method. 



Jefferson Physical Labokatort. 



