Recording Thermometers for Clinical Work. 549 



continued to rise appreciably for nearly ten minutes, 

 apparently indicating that the mouth had not been kept 

 closed long enough beforehand to reach a practically steady 

 temperature. 



A comparison of the records of the platinum tube thermo- 

 meter (Pt) and the Herseus quartz tube thermometer (He) 

 when placed in the mouth under similar conditions is shown 

 in fig. 3, which illustrates the importance of extreme quick- 

 ness and small thermal capacity in such tests. 



Fig. 3. 



Comparison of Quartz and Platinum Tube Thermometers in Mouth 

 after closure for 10 minutes. 



It might appear at first sight as though the slow and long 

 continued rise indicated by both thermometers in different 

 degrees, were due to the heating effect of the measuring 

 current, which might easily produce a result of this nature 

 if the current were excessive or the mass considerable. But 

 the current employed in taking these records scarcely 

 exceeded one hundredth of an ampere in the case of either 

 thermometer, and the heating effect of the current was 

 measured in both cases and found to be very small. With 

 the Herseus thermometer, when placed in a water-bath and 

 traversed by the same current, the rise of temperature due 

 to the passage of the current was found to be only 0°"085 C. 

 and to reach a steady value in about two minutes. When 

 enclosed in its metal protecting tube, so that the bulb of the 

 thermometer itself was surrounded by air instead of being in 

 direct contact with the water, the heating effect of the 

 current was increased to o, 31 C., and became steady in less 

 than three minutes. The comparatively high value of the 

 heating effect of the current with this thermometer is 

 evidently due to its small size and surface. When placed in 

 the mouth the heating effect of the current could not be 



