THE CALORIMETER. 37 



with the electric-resistance thermometers for the temperature of the air 

 and the walls and the body temperatures, and the deflections of the thermo- 

 electric elements. 



Numerous plans have been proposed for rendering automatic some of 

 these observations, as well as the control of the heating and cooling of the 

 air-circuits. Obviously, such a record of temperature measurements would 

 have two distinct advantages: (1) in giving an accurate graphic record 

 which would be permanent and in which the influence of the personal 

 equation would be eliminated; (2) while the physical observer at present 

 has much less to do than with the earlier form of apparatus, it would 

 materially lighten his labors and thereby tend to minimize errors in the 

 other observations. 



The development of the thread recorder and the photographic registration 

 apparatus in recent years led to the belief that we could employ similar 

 apparatus in connection with our investigations in this laboratory. To 

 this end a number of accurate electrical measuring instruments were pur- 

 chased, and after a number of tests it was considered feasible to record 

 automatically the temperature differences of the ingoing and outcoming 

 water from the calorimeter. Based upon our preliminary tests, the Leeds & 

 Xorthrup Company of Philadelphia, whose experience with such problems 

 is very extended, were commissioned to construct an apparatus to meet 

 the requirements of the respiration calorimeter. The conditions to be met 

 by this apparatus were such as to call for a registering recorder that would 

 indicate the differences in temperature between the ingoing and outcoming 

 water to within 0.5 per cent and to record these differences in a permanent 

 ink line on coordinate paper. Furthermore, the apparatus must be installed 

 in a fixed position in the laboratory, and connections should be such as to 

 make it interchangeable with any one of five calorimeters. 



After a great deal of preliminary experimenting, in which the Leeds & 

 Northrup Company have most generously interpreted our specifications, 

 they have furnished us with an apparatus which meets to a high degree of 

 satisfaction the conditions imposed. The thermometers themselves have 

 already been discussed. (See page 30.) The recording apparatus consists 

 of three parts: (1) the galvanometer; (2) the creeper or automatic sliding- 

 contact; (3) the clockwork for the forward movement of the roll of co- 

 ordinate paper and to control the periodic movement of the creeper. 



Under ordinary conditions with rest experiments in the chair calorim- 

 eter or bed calorimeter, the temperature differences run not far from 2° to 

 4°. Thus, it is seen that if the apparatus is to meet the conditions of the 

 specifications it must measure differences of 2° C. to within 0.01° C. Pro- 

 vision has also been made to extend the measurement of temperature differ- 

 ences with the apparatus so that a difference of 8° can be measured with the 

 same percentage accuracy. 



