172 A RESPIRATION CALORIMETER. 



The energy of an electric current is CE/ X io 7 ergs. , and this expressed 

 in calories at 10 is 



CE/? x io 7 ~~, _ , . . 



-j = CE/ x o. 23846 calories. 



4. 1935 x io 7 



But this is on the assumption that our electric units are o. i per cent 

 too small. Since we are using these same small units in our work, it is 

 evident that the numerical values of C and E are both too large by this 

 amount, and therefore the product too large by 0.2 per cent. This gives 

 0.23846 0.00048 = 0.2380 as the true conversion factor. 



We can reach the same result by taking the mean of the results for 

 the mechanical equivalent of heat obtained by Griffiths (4. 192), Schuster 

 and Gannon (4. 189), and Callendar and Barnes (4. 186) without correc- 

 tion for the supposed error in the electrical units. The mean of these 

 three values is J =4.189 X io 7 at 20. Correcting this to 10, we have, 

 multiplying by 1.003 as before, J = 4.2016 x io 7 at 10. Then 



CE/ X io 7 OT? . , , 



-j = LE/ x 0.2380, as before. 



4.2016 x io 7 



Thus no account need be taken of the supposed error in the electrical 

 units, inasmuch as the three English investigators above quoted all used 

 substantially the same electrical units that are now used in Middletown. 

 This value (0.2380) is slightly different from that used earlier 1 (0.2378), 

 because the latter is based on Griffith's value, which is somewhat larger 

 than the mean of the three used in this calculation. 



To compare this with the value given by Fischer and Wrede, it is 

 necessary to reduce to 15 and to correct for the difference between our 

 electrical units and those used in Germany. The first correction 

 amounts to 0.0019, giving 0.2380 x 1.0019= 0.23845. The second 

 amounts to 



= 0.0017. 



H340 



Thus 0.23845 x 1.0017 = - 23885, which is the proper value at 15 

 to use in Germany ; that is, with German electrical units. 



A value as large as 0.2394 can not, in the light of the most recent work, 

 be justified. 



As used by Jaeger and von Steinwehr it was apparently taken from 

 the values given by Graetz. 2 



1 U. S. Dept. of Agr., Office of Experiment Stations Bull. 63, p. 43. 



2 Winkelinann's Handbuch der Physik, 2, 2, p. 415. 



