A STUDY IN MO 1115 ID AND NORMAL P il Y .S I O L () U Y. 23 



In examining tliis tabic it will be seen that the first fonr narrow columns, after 

 the time record, are taken up with registers of temperature : the first of these repre- 

 sents tlie temperature of the air as it enters the box ; the secontl that of the air as 

 it leaves the box, both taken every fifteen minutes. Tlie figures at the bottom of 

 these two columns represent the respective averages, and it is plain that if the 

 smaller number be sul)tracted from the larger the average gain or loss of heat by 

 the air during its passage will be ascertained. Thus in the table given, the second 

 column, that of exit, gives an average of 67°. 14 ; whilst tlie first column, that of 

 entrance, gives an average of ()5°.6"2, showing that the air gained an average of 

 1°.52 during its passage. If, however, the average of the first cohunn had been 

 67°. 14, and that of the second 65°. 62, it would liave shown that the air had cooled 

 P. 52 during its passage. It is plain that the gain or loss of heat by the air in 

 flowing through the box must be respectively added to or subtracted from the heat 

 given to the calorimeter by the animal in order to determine the dissipation of heat 

 by the latter. To do this it is necessary that the calculation be made in heat units. 

 I have adopted the English unit of heat, namely, the amount of heat required to 

 raise one pound of water one degree Fahrenheit, because tlie scales of the various 

 instruments employed conform most readily with this standard. 



The amount of heat employed in elevating the temperature of any body is calcu- 

 lated by the Avell-known fornuila Q ^ W x t x sp. h., in whicli Q is the quantity 

 of heat employed, W the weight of tlie body, t the temperature which it is raised, 

 and sp. h. the specific heat of the body. In applying this formula to the air in the 

 experiments a difficulty presented itself. The quantity of the air which has passed 

 tlirough the box and been cooled or heated is easily known. The first broad column 

 of the table gives the readings of the general meter before and after tlie experi- 

 ment ; subtracting the first number from the second gives the amount of air which 

 has passed through the large general meter; add to this the amount wliich has 

 passed througli the sample meter (registered in second broad column), and the 

 whole quantity of air which has been drawn through tlie box is known. The weight 

 of a cubic foot of air at 32° F. is 0.08073 lb. Tlie air in the box is of various 

 temperatures in ditterent experiments, and is always much expanded by the heat ; 

 hence it is necessary to reduce by calculation the volume of the air to what it 

 would be if the box were cooled to 32° F. In doing this I have considered the 

 temperature of the air of the box as that at which it emerges. This is not 

 strictly correct, but the error is so small as to be of no possible importance. Taking 

 then this temperature, and using the following letters to signify as given below, 

 tlie calculation becomes a simple one. V = quantity of air in cubic feet at 32°. 



V = known quantity of air at a known temperature, t' = number of degrees this 

 quantity is heated above 32°. Then V + [Vx t'x 0.002035 (coefficient of expan- 

 sion)] = v. Using as a type the experiment recorded above, we have 



V =83.475. t'=67°.U — 32° =35.14. V +(Vx 35.14 XO.002035) = 83.475. 



V + 0.0715 V = 83.475. V = ^^tj^ = 77.9 cub. ft. 

 ' 1.0/15 



The quantity of air at 32° being known, tlie weight is readily ascertained : _ 

 W = Vx 0.08073 (weight of 1 cubic foot at 32° F.) = 6.289 lbs. 



