THE CALORIMETER. 31 



In the case of the thermometer which measured the outcoming water, 

 the difficulty was not so great, as the outcoming water is somewhat nearer 

 the temperature of the chamber, and the water as it leaves the thermometer 

 passes first over the mercurial thermometer and then over the resistance 

 thermometer. By means of a long series of tests it was found possible to 

 adjust these resistance thermometers so that the variations in resistance 

 were in direct proportion to the temperature changes noted on the mercu- 

 rial thermometers. Obviously, these differences in resistance of the two 

 thermometers can be measured directly with the Wheatstone bridge, but, 

 what is more satisfactory, they are measured and recorded directly on a 

 special type of automatic recorder described beyond. 



OBSERVER'S TABLE. 



The measurements of the temperature of the respiration chamber, of the 

 water-current, and of the body temperature of the man, as well as the heating 

 and cooling of the air-spaces about the calorimeter, are all under the control 

 of the physical assistant. The apparatus for these temperature controls 

 and measurements is all collected compactly on a table, the so-called " ob- 

 server's table." At this, the physical assistant sits throughout the experi- 

 ments. For convenience in observing the mercurial thermometers in the 

 water-current and general inspection of the whole apparatus, this table 

 is placed on an elevated platform, shown in fig. 3. Directly in front of the 

 table the galvanometer is suspended from the ceiling and a black hood 

 extends from the observer's table to the galvanometer itself. On the ob- 

 server's table proper are all the electrical connections and at the left are the 

 mercurial thermometers for the chair calorimeter. Formerly, when the 

 method of alternately cooling and heating the air-spaces was used, the 

 observer was able to open and close the water-valves without leaving the 

 chair. 



The observer's table is so arranged electrically as to make possible tem- 

 perature control and measurement of either of the two calorimeters. It is 

 impossible, however, for the observer to read the mercurial thermometers 

 in the bed calorimeter without leaving his chair, and likewise he must 

 occasionally alter the cooling water flowing through the outer air-spaces 

 by going to the bed calorimeter itself. The installation of the electric- 

 resistance thermometers connected with the temperature recorder does away 

 with the reading of the mercurial thermometers, save for purposes of com- 

 parison, and hence it is unnecessary for the assistant to leave the chair at 

 the observer's table when the bed calorimeter is in use. Likewise the sub- 

 stitution of the method of continuously cooling somewhat the air-spaces 

 and reheating with electricity, mentioned on page 18, does away with the 

 necessity for alternately opening and closing the water-valves of the chair 

 calorimeter placed at the left of the observer's table. 



