The calculation of the heat developed in the apparatus is made by means of the formula C × E × _t_ × 0.2385 = calories, in which C equals the current in amperes, E the electromotive force, and _t_ the time in seconds. This gives the heat expressed in calories at 15° C. This procedure we have followed as a result of the recommendation of Dr. E. B. Rosa, of the National Bureau of Standards. In order to convert the values to 20°, the unit commonly employed in calorimetric work, it has been necessary to multiply by the ratio of the specific heat of water at 15° to that of water at 20°. Assuming the specific heat of water at 20° to be 1, the specific heat at 15° is 1.001.[16] Of the many electrical check-tests made with this type of apparatus, but one need be given here, pending a special treatment of the method of control of the calorimeter in a forthcoming publication. An electrical check-experiment with the chair calorimeter was made on January 4, 1909, and continued 6 hours. The voltmeter and mil-ammeter were read every few minutes, the water collected in the water-meter, carefully weighed, and the temperature differences as measured on the two mercury thermometers were recorded every 4 minutes. The heat developed during the experiment may be calculated from the data as follows: Average current = 1.293 amperes; average E. M. F. = 109.15 volts; time = 21,600 seconds; factor used to convert watt-seconds to calories = 0.2385. (1.293 × 109.15 × 21600 × 0.2385) × 1.001 = 727.8 calories produced. During the 6 hours 237.63 kilograms of water passed through the absorbing system. The average temperature rise was 3.04° C., the total heat brought away was therefore (237.63 × 3.04) × 1.0024[17] = 724.1 calories. Thus in 6 hours there were about 3.7 calories more heat developed inside the apparatus than were measured by the water-current, a discrepancy of about 0.5 per cent.