Nov. 22, 1915 
Improved Respiration Calorimeter 
337 
The temperature of the zinc wall is kept as nearly as possible like that 
of the copper wall, so that the deflections of the galvanometer connected 
with the differential thermoelements in the walls are as close as possible 
to o. Even under the most favorable conditions it is hardly practicable 
to keep the two walls so uniformly alike that there will be no deflection 
at any time, because the temperature of the copper wall, however well 
regulated, does vary to some extent, and it is not possible to anticipate 
the change. It is possible, however, to keep the deflections most of the 
time so small that any error introduced by the temperature differences 
which they indicate would be insignificant. As explained on page 334, 
the number of thermoelements in each section of the walls and the sen¬ 
sitivity of the galvanometer are such that a very small difference between 
the temperature of the copper wall and that of the zinc wall would cause 
a fairly large deflection; hence, a very small deflection really means a 
practical identity of temperature of the two walls. When the rate of 
production of heat within the chamber is quite uniform and the rate of 
abstraction of heat is so nearly like it that the temperature conditions 
within the chamber are quite constant, the temperature of the zinc wall 
may be kept so nearly like that of the copper wall that the deflection 
will not exceed 5 mm. and will generally be less. A deflection of that 
magnitude would indicate for the bottom section a difference not greater 
than 0.005 degree between the average temperature of the copper floor of 
the chamber and that of the zinc wall outside of it; for the other sections 
it would indicate still smaller differences. The amount of heat gained 
by either wall from the other with such small differences is of little im¬ 
portance in comparison with the total amounts usually measured in the 
chamber. In an experiment with a variable heat production, as would 
be the case with a man moving and quiet by turns, such a close balance 
could hardly be maintained at all times, though the deviation need not 
greatly exceed 5 mm. for any considerable periods. Furthermore, it is 
possible to make the deflections in one direction equal to those in the 
other direction for equal short periods, so that whatever heat may be 
gained by the copper wall from the zinc wall during one period is counter¬ 
balanced by that gained by the zinc wall from the copper wall during the 
succeeding period, in which case there is no actual increase or decrease 
of the quantity of heat in the chamber for the total time of the two 
periods due to an exchange of heat between the walls. 
In order that the walls controlled in the manner described shall be 
heatproof, their temperature and that of the iron structure between 
them must be the same. The temperature of the copper wall, and con¬ 
sequently that of the zinc wall, is governed by that of the air in the 
chamber; but the two walls may be brought into thermal equilibrium 
at a temperature above or below that of the framework, in which case 
the quantity of heat in the chamber would probably be affected by the 
