Nov. 22. I9IS Improved Respiration Calorimeter 331 



Atwater and Rosa, to prevent gain or loss of heat through the walls, 

 though with modifications in details which make the present apparatus 

 exceedingly sensitive, while easy to operate. The copper wall * of the 

 chamber is duplicated by a wall of zinc attached to the outside of the 

 iron framework which supports the copper wall, as explained on page 303, 

 and the temperature of the zinc wall is regulated to accord with that of 

 the copper wall in such manner that the thermal conditions of the two 

 walls will be in equilibrium with each other. When the temperature of 

 the zinc wall is the same as that of the copper wall, the quantity of heat 

 transmitted from each wall to the other is the same, so that neither wall 

 actually gains heat from the other. The effect of such a condition on 

 the quantity of heat in the chamber would be the same as if no heat were 

 to pass from either wall to the other in either direction. If the tempera- 

 ture of the zinc wall is above that of the copper wall, the quantity of 

 heat passing from the zinc to the copper is greater than that in the reverse 

 direction — i. e., the copper wall will gain heat from the zinc wall, some 

 of which, at least, it will transmit to the air of the chamber. Con- 

 versely, if the temperature of the zinc wall is below that of the copper 

 wall, the former will gain heat from the latter, some or all of which the 

 copper wall has derived from the air of the chamber. If the quantity of 

 heat which the copper wall has gained from the zinc wall is counter- 

 balanced by an equal quantity gained by the zinc wall from the copper 

 v.-all, the effect on the measurement of the quantity of heat produced in 

 the chamber is the same as if no heat had been transferred from either 

 wall to the other. This counterbalancing may be accomplished by 

 keeping the temperature of the zinc wall above or below that of the 

 copper wall, as need be, to the same degree and for the same length of 

 time that the conditions were reversed. For this purpose means are 

 provided for determining when the zinc wall is warmer or colder than the 

 copper wall, and for heating and cooling the zinc wall as is found necessary. 



Detecting Differences in Temperature of" the Double Metal Walls 

 Thermoelectric thermometers are used to detect any difference between 

 the temperature of the zinc wall and that of the copper wall. Differential 

 thermoelements are installed between the two walls, with the junctions 

 at one end of each element close to the outer surface of the copper wall, 

 while those of the other end are in the plane of the zinc wall, and the 

 terminals of the elements are connected with a sensitive galvanometer. 

 The direction of the deflection of the galvanometer indicates whether the 

 zinc wall is warmer or cooler than the copper wall — i. e., whether to 

 warm or to cool the zinc wall. 



Each thermoelement consists of four copper-constantan couples made of 

 bare hard-drawn wire about i mm. in diameter (No. 18, American gauge). 

 In making the junctions, the copper and constantan wires were put end 



' As used in this section, the term "wall" may include the ceiling and the floor as well as the side walls. 



9841°— 15 3 



