THE HUMAN BODY AN INACCURATE THERMOSCOPE. 283 



very cold metallic substances produce the same effect on the skin 

 as hot ones; i.e., they produce pain and a "burn" or % blister, on 

 account of the destructive action of unduly low or high temperatures 

 on the living tissues* ; but even without going to such extremes 

 as these, it may be easily shown that the human body will have a 

 sensation of warmth or coldness communicated to it by one and the 

 same object according to the condition in which it has been placed 

 previously. Arrange three basins on a table side by side ; in the 

 left hand one place water with some lumps of ice, so as to chill it 

 as much as possible ; in the right hand one put water as hot as 

 the hand will bear without being scalded; in the middle one 

 put a mixture of equal bulks of the hot and cold water, so that 

 the temperature here may be intermediate. Now stand with the 

 left hand in the left hand basin, and the right hand in the right 

 hand basin ; and after a minute or two, when each hand respec- 

 tively has become somewhat accustomed to the water in which 

 it is immersed, lift them out of the basins and place them both in 

 the middle basin ; the lukewarm water therein will feel quite cool 

 to the right hand that has previously been in much hotter water ; 

 but to the left hand it will seem distinctly warm by contrast with 

 the ice cold water in which it was previously immersed. "With 

 three buckets of water the feet and legs may be similarly used. 



Thermometers and such like non-vitalised instruments, however, 

 show no such irregularity ; a thermometer placed in the hot water 

 will sink on transference to the middle basin, whilst one previously 

 immersed in the ice water will rise on being placed therein ; but 

 each of the two will register the same temperature when they 

 have stood a while in the lukewarm water, which will not seem 

 warm to the one and cold to the other as it does to the human 

 nerves of sensation. 



The following Table indicates some of the most remarkable 

 centigrade temperatures connected with various phenomena, ranging 

 from the lowest to the highest : 



Absolute zero (theoretical), . . . - 273 C. 



Greatest recorded natural cold of Arctic regions, . - 50 



Freezing point of mercury, - 40 



Fahrenheit's zero (temperature of snow and salt), . - 17'8 



Melting point of ice, 



Point of maximum density of water (Expt. 315), . +4 



Blood heat, 36 to 37 



Boiling point of water at normal pressure, . . 100 



Do. mercury, 350 



Do. sulphur, . . . . 420 



* "The parching wind burns frore (i.e., freezingly), and cold performs the 

 effect of fire." Milton's Paradise Lost. 



