Nov. 22. 1915 Improved Respiration Calorimeter 323 



observations were recorded. This method afforded opportunity for 

 errors in fundamental data, some of which might be obvious, but most 

 of which would not be detected. 



MEASUREMENT BY ELECTRIC-RESISTANCE THERMOMETERS 



To relieve the observer of the tedium of these observations, and 

 especially to eliminate as much as possible of the personal element 

 from the measurement, the mercury thermometers were replaced by a 

 device for measuring the increase in the temperature of the water by 

 the difference in electrical resistance of two coils of wire in the water 

 circuit. Atwater and Rosa (4, p. 25; 5, p. 151) employed a device of 

 this character in their original calorimeter, but did not develop it to 

 measure temperature differences with the same degree of accuracy as 

 the one here described. The latter device comprised two special resist- 

 ance coils, a special Kohlrausch bridge, a sensitive galvanometer, and a 

 lamp and scale for reading the deflections of the galvanometer. The 

 specially mounted resistance coils, called the "bulbs," were inserted in 

 the water line where the bulbs of the mercury thermometers had been 

 and were connected with the special Kohlrausch bridge on the observer's 

 table, the two coils being in opposite branches of the bridge circuit, with 

 the slide wire between them. The reflecting D' Arson val galvanometer 

 by which the bridge was shown to be balanced was suspended in such a 

 position that the scale on which the deflections of the galvanometer 

 were read was on a level with and directly in front of the eyes of the 

 observer sitting at the table. The movement of the galvanometer was 

 indicated by the movement of a vertical line of light along the scale, 

 the light from a straight-filament electric lamp being reflected by the 

 mirror of the galvanometer. To determine the difference in the tem- 

 perature of the two coils, it was merely necessary to move the battery 

 circuit contact along the sUde wire of the bridge until the line of light 

 was at the center of the scale, showing that the bridge was balanced. 

 The reading of the bridge scale was then recorded. To balance the 

 bridge and read its scale was much more convenient than to read the 

 mercury thermometers, and only one record was involved. 



Several types of resistance-thermometer bulb were tried in connection 

 with this device. In one, insulated resistance wire was incased in a coil 

 of small-bore lead tube, which was immersed in an enlargement in the 

 water channel. This proved unsatisfactory for several reasons. One 

 was that it did not respond quickly enough to changes in the temperature 

 of the water, owing probably to poor thermal contact between the wire 

 and the tube; and the mass of metal in the tube also tended to increase 

 the lag. Another was that the space in the lead tube was not deprived 

 of water vapor, and this eventually moistened the insulation of the resist- 

 ance wire, so that a short circuit was established between the wire and the 



