222 THE HUMAN BODY. 



body whether its temperature is the same, or whether it is 

 higher or lower than the point of skin which touches it; in 

 other words, touch gives us an idea of the relative tempera- 

 ture of bodies. But the sensation may change in a few 

 moments, as the object in contact with the skin rapidly im- 

 parts or borrows heat; and if it is warmer or colder than the 

 skin, an equilibrium is soon established when the difference 

 is inconsiderable. And the same body may produce a sensa- 

 tion of cold or heat successively without change of tempera- 

 ture, according as the surface of the skin at the moment of 

 contact is warm or cold; thus, if we take a bath in water 

 cooler than the air, the temperature of the air, which seemed 

 low on entering the bath, appears warm when we come out 

 a few minutes after. It is for the same reason that we find 

 the air of a cellar cool in summer, and warm in winter, 

 although it has not varied. 



The sensation is marked in proportion to the conducting 

 quality of the object in contact with the skin. Air seems 

 warmer than water at the same temperature, because the air 

 being a worse conductor of heat takes less from the skin in a 

 given time. Air in motion, by exciting evaporation, causes 

 a very sensible loss of heat, as every one knows; and the 

 atmosphere also, which seems very cold when the wind blows, 

 grows warmer apparently when the wind ceases, or when we 

 are sheltered from it. 



The contrary effect from that caused by pressure is here 

 seen; the sensation is marked in proportion to the extent of 

 surface. The whole hand appreciates the temperature better 

 than a single finger; and a body of a given temperature, 

 applied over a large surface, will give a sensation of more 

 intense heat than a warmer body which touches only a small 

 portion of skin. We can easily understand that the skin 

 absorbs in a given time more heat by a surface four inches 

 square, than by one only one inch square, and the impression 

 transmitted to the brain in this experiment represents rather 

 the sum of the heat absorbed from all parts of the surface in 

 contact, than the temperature of the body with which the 

 experiment is made. 



When we touch a body of a lower temperature, the same 



