28 



Messrs. Morton, Mayer, and Thomas on 



III. Determination of current-strength in circuit correspond- 

 ing to various intensities of luminous power in lamp and of 

 deflections of galvanometer. — For these determinations the 

 apparatus was arranged as follows : — The battery-current was 

 passed through one coil of a Gaugain galvanometer, then 

 through a copper voltameter, and then through the lamp placed 

 in the photometer, thence returning to battery. 



The amount of copper deposited in a known time gave of 

 course the current-strength, in view of the fact that a current 

 of one weber deposits *326 milligramme of copper in a second. 



Thus, in the first experiment, 1062*4 milligrammes were 

 deposited in an hour, or in 3600 seconds ; therefore 



1062-4 

 •326 x 3600 



= '905 weber current. 



Three experiments were made of this sort, the data and 

 results of which are given in the following Table : — 



Weights of cathode. 



Time. 



Current, in 

 webers. 



Maximum 

 candle- 

 power. 



Before. 



After. 



Gain. 



43398-4 44460-8 

 48314-0 | 49110-0 

 43105-0 | 43617-0 



1062-4 

 796-0 

 512-0 



60 min. 

 40 „ 

 25 „ 



•905 

 1-017 

 1-047 



15 

 17-6 

 • 198 



From the current in webers and the corresponding resistance 

 in ohms, where these had been determined as above, it was of 

 course easy to deduce the exact amount of energy transformed 

 into light and heat, and to compare the same with the actual 

 candle-power afforded by the lamp at the same time*. 



To make the results more general, however, the constant 

 for the tangent-galvanometer used in all the experiments was 

 determined so that the current-strength corresponding to its 

 readings could be obtained in the cases where the voltameter 

 had not been employed. This constant was found to be '262 ; 

 so that the tangent of the galvanometer-reading multiplied by 

 '262 gave the current-strengths in all cases. 



* Thus, for example, in one experiment the average candle-power being 

 10+ candles, the resistance of the lamp was 76 ohms and the current 

 *90o weber. 



