136 Domestic Science 



give the same opinion with regard to the same body 

 in. the same condition with respect to its hotness. A 

 frequently quoted experiment may be performed in 

 illustration of this. 



EXPERIMENT 45. Procure three bowls, such as, are 

 in common use for kitchen purposes. In one pour some 

 water as hot as the hand is capable of bearing, into 

 the second some cold water from the tap, and into the 

 third a mixture of equal parts of the hot and cold water. 

 Put the right hand into the hot water, and the left 

 into the cold. Allow each hand to remain in the water 

 until no special feeling of heat or cold is to be noticed 

 in either case. Remove the hands and plunge both 

 into the third bowl. The right hand will provide the 

 information that the water in this bowl is cool, while 

 the left gives the impression that the same water is 

 distinctly warm. 



From what has been shown in this experiment it 

 is clear that one's bodily sensations are not trustworthy 

 guides in the matter of measuring the degree of hotness 

 of a body. Many instruments have been devised by 

 which this measurement may be effected with greater 

 accuracy, the one in most general use being the mercury 

 thermometer. (Gr. thermos, heat.) In this instrument 

 and in the alcohol thermometer advantage is taken of our 

 earlier observation to the effect that liquids in general 

 expand under the influence of heat to a greater extent 

 than solids. 



89. A thermometer consists essentially of a long 

 glass tube of fine bore, upon one end of which a bulb 

 has been blown, and the other end of which is sealed. 

 At ordinary temperatures the bulb and part of the 

 stem are filled with mercury, the remainder of the stem 

 being empty, save for a minute quantity of the vapour 



