Temperature. Thermometers 149 



and thus neither becomes hotter than at first. It will 

 be noticed that during the passage of heat from a hot 

 body to a colder one, the temperature of the hot body 

 diminishes, while that of the cold one increases. This 

 continues till both bodies are at the same temperature. 

 Thus, when we determine the temperature of a body 

 by placing a thermometer in contact with it, the 

 instrument receives heat, if the body be warm, and 

 the final temperature recorded on the thermometer will 

 be that at which the quantities of heat interchanged 

 are equal. This will be evidently slightly 

 lower than the original temperature of the 

 body, but the error will in general be small, 

 since most bodies treated in this way are 

 considerably larger than the thermometer 

 and the amount of heat lost in warming up 

 the thermometer is comparatively little. This 

 point will be more clearly grasped after reading 

 the next chapter. 



95. Two useful modifications of the ordi- 

 nary thermometer merit special description. 

 The clinical thermometer, of which Fig. 47 is an 

 illustration, has a scale of short range, usually 

 from 95 F. to 1 10 F. The degrees are further 

 divided into fifths or tenths of a degree. The 

 bore of the instrument is small, and, in order 

 to enable the position of the end of the fine 

 mercury thread to be read with ease, the shape 

 of the section of the glass tube is such that 

 the glass has a magnifying effect. A short Fig. 47. 

 distance above the bulb of the instrument 

 the bore of the tube is narrowed considerably. The 

 purpose of this constriction is to prevent the mercury, 

 which has passed into the part of the tube on which 



