THE CALORIMETER. 29 



type of construction gives maximum sensibility to the temperature fluctua- 

 tions of the air itself and yet insures thorough protection. The two termi- 

 nals are carried outside of the respiration chamber to the observer's table, 

 where the temperature fluctuations are measured on a Wheatstone bridge. 



WALL THERMOMETERS. 



The wall thermometers are designed for the purpose of taking the tem- 

 perature of the copper wall rather than the temperature of the air. When 

 temperature fluctuations are being experienced inside of the respiration 

 chamber, the air obviously shows temperature fluctuations first, and the 

 copper walls are next affected. Since in making corrections for the hydro- 

 thermal equivalent of the apparatus and for changes in the temperature 

 of the apparatus as a whole it is desirable to know the temperature changes 

 of the wall rather than the air, these wall thermometers were installed for 

 this special purpose. In construction they are not unlike the thermometers 

 used in the air, but instead of being surrounded by perforated metal they 

 are encased in copper boxes soldered directly to the wall. Five such ther- 

 mometers are used in series and, though attached permanently to the wall, 

 they are placed in relatively the same position as the air thermometers. The 

 two terminals are conducted through the metal walls to the observer's table, 

 where variations in resistance are measured. The resistance of the five 

 thermometers is not far from 20 ohms. 



ELECTRICAL RECTAL THERMOMETER. 



The resistance thermometer used for measuring the temperature of the 

 body of the man is of a somewhat different type, since it is necessary to 

 wind the coil in a compact form, inclose it in a pure silver tube, and con- 

 nect it with suitable rubber-covered connections, so that it can be inserted 

 deep in the rectum. The apparatus has been described in a number of 

 publications.* The resistance of this system is also not far from 20 ohms, 

 thus simplifying the use of the apparatus already installed on the observer's 

 table. 



ELECTRIC-RESISTANCE THERMOMETERS FOR THE WATER-CURRENT. 



The measurement of the temperature differences of the water-current by 

 the electric-resistance thermometer was tried a number of years ago by 

 Eosa,f but the results were not invariably satisfactory and in all the sub- 



* Benedict and Snell: Eine neue Methode um Korpertemperaturen zu messen. 

 Archiv f. d. ges. Physiologic, Bd. 88, pp. 492-500. (1901.) 



W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances 

 for the direct determination of oxygen. Carnegie Institution of Washington 

 Publication No. 42, p. 156. (1905.) 



fRosa: U. S. Dept. of Agric., Office of Experiment Stations Bui. 63, p. 25. 



