34 CALORIMETERS FdR STUDYING RESPIRATORY EXCHANGE, ETC. 



tures in the various parts, and while the algebraic sum of the temperature 

 differences of the parts may equal zero, it is conceivable that there may be 

 a condition in the calorimeter when there is a considerable amount of heat 

 passing out through the top, for example, compensated exactly by the heat 

 which passes in at the bottom, and while with the top section there would be 

 a large plus deflection on the galvanometer, thus indicating that the air 

 around the zinc wall was too cold and that heat was passing out, there 

 would be a corresponding minus deflection on the bottom section, indicat- 

 ing the reverse conditions. The two may exactly balance each other, but 

 it has been found advantageous to consider each section as a unit by itself 

 and to attempt delicate temperature control of each individual unit. This 

 has been made possible by the electrical connections, as shown on the 

 diagram. 



RHEOSTAT FOR HEATING. 



The rheostat for heating the air-spaces and the returning air-current 

 about the zinc wall is placed on the observer's table and is indicated in the 

 diagram as E 2 . There are five different sets of contact-points, marked 1, 2, 

 3, 4, and 5. One end of the rheostat is connected directly with the 110- 

 volt circuit through the main switch S 5 . The other side of the switch S 5 

 connects directly with the point on the middle of switch S 10 , and when this 

 middle point is joined with either f and F, direct connection is insured 

 between all the various heating-circuits on the calorimeter in use. The 

 various numbered points on the rheostat R 2 are connected with the binding 

 posts on S 10 , and each can in turn be connected with a or A, & or B, etc. 

 The heating of the top of the chair calorimeter is controlled by the point 5 

 on the rheostat E 2 , the rear by the point 4, the front by the point 3, and 

 the bottom by the point 2. Point 1 is used for heating the air entering the 

 calorimeter by means of an electric lamp placed in the air-pipe, as shown 

 in fig. 25. 



The warming of the electrical reheater placed in the water-circuit just 

 before the water enters the calorimeter is done by an electrical current con- 

 trolled by the resistance R x . This R x is connected on one end directly with 

 the 110-volt circuit and the current leaving it passes through the resistance 

 inside the heater in the water-current. The two heaters, one for each calo- 

 rimeter, are indicated on the diagram above and below the switch S 9 . The 

 disposition of the switches is such as to make it possible to use alternately 

 the reheaters on either the bed or the chair calorimeter, and the main 

 resistance R a suffices for both. 



WHEATSTONE BRIDGES. 



For use in measuring the temperature of the air and of the copper wall 

 of the calorimeters, as well as the rectal temperature of the subject, a series 



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