342 Journal of Agricultural Research voi. v.no.s 



Heat from Other Sources 



The store of heat in other objects in the chamber than the body of the 

 subject — e. g., furniture — is increased by a rise and decreased by a fall 

 in the temperature of the air surrounding them, and allowance must be 

 made for the effect of such change in their condition upon the measure- 

 ment of the quantity of heat produced in the chamber. The quantity 

 of heat involved is computed from the weight, the specific heat, and the 

 change in the temperature of the objects. The latter factor is not 

 definitely known, however, as no provision is made for actually measur- 

 ing the temperature of such objects; the assumption being that their 

 change in temperature will be the same as that of the air, which is deter- 

 mined. Where the change occurs slowly, any error involved in such 

 assumption is probably negligible; but this is not true when any con- 

 siderable change occurs in a short period. This is another reason for 

 keeping the temperature of the air of the chamber as constant as possible. 



Allowance must be made also for gain or loss of heat due to the intro- 

 duction of objects into the chamber at a temperature above or below 

 that of the air. Hot food or drink, for example, admitted through the 

 food aperture would add heat to that produced in the chamber, while 

 cold material would absorb some of the heat produced. The tempera- 

 ture at which any material is admitted is recorded, together with its 

 weight and character, and from these data, with the specific heats of 

 the various articles, the necessary corrections are computed. 



The electric fan by which the air of the chamber is agitated and the 

 electric light, when one is used, both generate heat which forms part of 

 that measured by the calorimeter and for which allowance must be made. 

 The quantity of heat produced is computed according to the formula 



Elt 

 - — 5- = small calories at 20° C, E being the voltage and / the amperage of 

 4-io3 , 



the current in the lamp and the fan, and t the time in seconds during 

 which it was used. 



The divisor, 4.183, is the number of international joules (watt seconds) 

 equivalent to one small calorie at 20° C. (10, p. 255). The lamp and fan 

 are connected in such manner that the voltage and amperage of both 

 may be determined at the same time by calibrated measuring instru- 

 ments on the observer's table, the readings of which are recorded at 

 regular intervals. That the heat may be generated at a uniform rate, 

 the current is taken from a generator which has an automatic regulator 

 to keep the voltage constant within quite narrow limits. 



APPARATUS FOR MEASURING MUSCULAR WORK PERFORMED BY THE 



SUBJECT OF AN EXPERIMENT 



For the study of many problems involving the performance of muscu- 

 lar work some method of measuring the amount of work done is requi- 

 site. An apparatus (9, p. 48; 8, p. 11) that was devised in connection 

 with the nutrition investigations of the Department has proved very 



