12 TEMPERATURE FLUCTUATIONS IN THE HUMAN BODY. 



ture difference between the two junctions. This might be assumed to be 

 approximately proportional to the voltage, but can be obtained directly by 

 keeping both junctions at known temperatures; in this way the apparatus 

 can be calibrated so that different settings of the contact correspond to 

 definite values of the temperature difference being measured. In order to 

 make the apparatus direct reading, an additional resistance in series with 

 the battery is almost universally used and the current is so adjusted as to 

 accommodate itself to the particular slide-wire available. By bringing the 

 current to such a value that the fall in potential across one division of C-D 

 is equal to the voltage of the thermal-junction system for a temperature 

 difference of 0.01 C, the apparatus becomes practically direct reading in 

 hundredths of a degree. 



ADAPTATION OF METHOD FOR USE. 



The actual arrangement, as shown in fig. 2 (p. 15), does not differ in principle 

 from this. The storage battery B, which has been partly discharged in order 

 to obtain a more nearly constant voltage, sends current continuously through 

 the circuit B-R-Vi-V 2 -V 3 -V 4 -S in parallel with P-M-B. The resistance R is 

 fixed, and is placed in the circuit for the purpose of bringing the current to such 

 a value that the apparatus is practically direct reading; Vi, V 2 , V 3 , and V 4 are 

 variable resistances by means of which the current can be maintained constant 

 in spite of slight changes in the electromotive force of the storage cell, such as 

 might be caused by a gradual discharging of the cell, temperature changes, etc. 

 The shunt S is placed across the potentiometer P on account of the extremely 

 low voltages to be measured. The resistance M is so arranged that the stand- 

 ard cell N and galvanometer G can be closed across it, this arrangement forming 

 the equivalent of a very accurate ammeter, so precise that a high resistance 

 O is introduced into its circuit to reduce the sensitiveness. Since the galva- 

 nometer must be used in connection with both the standard cell and the 

 thermal-junction circuits, the switches Gi and G 2 are provided for transferring 

 it from one to the other. By means of the test switch T, the apparatus may 

 be tested for stray electromotive forces. The control switch K is used for 

 convenience in bringing the galvanometer to rest. The switches 1, 2, 3, 4, etc., 

 are also provided so that the electromotive force of any one of a number of 

 thermal-junction systems may be measured. To each of these switches are 

 connected two copper wires, one of which runs to the body and the other to a 

 constant-temperature bath, these latter terminals being connected by a con- 

 stantan wire, which furnishes the second metal for the thermal junctions. 



APPARATUS USED IN THE RESEARCH. 

 CONSTANTS OF THE APPARATUS. 



While considering the measurement from a purely theoretical standpoint, 

 and before proceeding to a description of the actual construction, it may be 

 well to bring together the constants of such parts of the apparatus as were 

 available for the work, and to include the computations by means of which 



