26 TEMPERATURE FLUCTUATIONS IN THE HUMAN BODY. 



potentiometer setting would have been greater had it not been for the presence 

 of this extraneous electromotive force, and so the correction must be added. 

 The actual magnitude of the stray correction is determined from the galvan- 

 ometer sensitiveness and the average stray deflection. The sensitiveness 

 of the galvanometer has been found by trial to be such that when taking the 

 stray correction which necessitates setting the potentiometer at a 

 deflection of 25 millimeters corresponds to a change in the potentiometer 

 setting of 1 ohm, so that a deflection of 1 millimeter corresponds to a change 

 in setting of 1 -f- 25 or 0.040 ohm. The average stray deflection in the calibra- 

 tion just given is 3.1 millimeters. This, it is seen, is equivalent to a change in 

 setting of 0.040X3.1 or 0.12 ohm, which is therefore the correction that must 

 be added to the setting on account of the stray electromotive force. 



When taking the readings of the thermal junctions, the potentiometer 

 setting is no longer 0, but is increased in the present instance to 18 ohms. 

 This change increases the resistance of the galvanometer circuit and thus 

 reduces its sensitiveness, so that under the new conditions a deflection of 

 1 millimeter has been found by trial to correspond to a change in setting of 

 0.063 ohm. As before, a positive deflection is equivalent to a decreased 

 balance. Thus, the final corrected balances for the different junctions are: 



A, 1S.00+0.12+2.7X0.063 = 1S.29 



B, 18.00+0.12-2.6X0.063 = 17.96 



C, 18.00+0.12-4.9X0.063 = 17.81 



D, 18.00+0.12-2.7X0.063 = 17.95 



E, 18.00+0.12-0.1X0.063 = 18.11 



F, 18.00+0.12-4.9X0.063 = 17.81 



G, 18.00+0.12-4.8X0.063 = 17.82 



The temperature difference is determined from the average readings of the 



two Beckmann thermometers, one in the constant-temperature oven, the other 



in the calibrating flask. The temperature in the constant-temperature oven 



is given by the formula previously deduced: 1 



Temperature in oven = 37 . 300 + 1 . 008 X reading 



= 37. 300 + 1. 00SX2. 459=39. 779 C. 



Similarly the temperature in the calibrating flask is given by the formula: 



Temperature in flask = 34 . 365 + 1 . 009 X reading 



= 34.365 + 1.009X3.761=38.160 C. 



The temperature difference is then : 



39.779-38.160 = 1.619 C. 



The potentiometer balance corresponding to a certain temperature difference 

 has now been obtained for each of the several thermal junctions, and this 

 temperature difference accurately determined by means of the two mercury 

 thermometers. A knowledge of the relation between these two quantities 

 (1) potentiometer balance and (2) temperature difference, is the sole object 

 of calibrating. This relation was determined for a number of temperature 

 differences and the results expressed in a number of curves, one for each 

 junction. These curves are very nearly straight lines for the range and pre- 



'See p. 23. 



