HEAT. 207 



When do we lower than that of the hand, heat, in accord- 

 caiiabodycoid? q^^^q ,^yj|-jj ^|^q saiDC lavv, passcs out from the 



hand to the body touched, and occasions the sensation 

 which we call cold,* 



461. Sensations of heat and cold are, therefore, merely 

 degrees of temperature, contrasted by name in reference 

 to the peculiar temperature of the individual speaking of 

 them. 



A body may feel liot and cold to the same person at the 

 circumstances Same time, since the sensation of heat is produced by a body 

 may abody feel colder than tlie hand, provided it be less cold than the body 

 the same per- touched immediately before ; and the sensation of cold is 

 tUne?*^ ^^^^ produced under the opposite circumstances, of touching a 

 comparatively warm body, but which is less warm than somo 

 other body touched previously. Thus, if a person transfer one hand to com- 

 mon spring water immediately after touching ice, to that hand the water 

 would feel very warm ; while the other hand transferred from warm water 

 to the spring water, would feel a sensation of cold. 



Has heat 462. Heat is imponderable, or does not pos- 



weight? gggg g^j^y. perceptlblc weight. 



If we balance a quantity of ice in a delicate scale, and then leave it to 

 melt, the equilibrium will not be in the sliglitest degree disturbed. If we 

 substitute for the ice boiling water or red-hot iron, and leave this to cool, 

 there will be no diiferenco in the result. Count Rumford, having suspended 

 a bottle containing water, and another containing alcohol to the arms of a 

 balance and adjusted them so as to be exactly in equilibrium found that the 

 balance remained undisturbed when the water was completely frozen, though 

 the heat the water had lost must have been more than suEBcient to have made 

 an equal weight of gold red hot. 



What do we 463. The nature, or cause of heat is not 

 nat'uTeofhe*a\^? clcarly Understood. Two explanations, or 

 theories have been proposed to account for the 

 various phenomena of heat, which are known as the me- 

 chanical and vibratory theories. 



Explain theme- ^64. Tlic mcclianical theory supposes herb 

 chanicai theory. ^^ ^^ ^^^ cxtrcmcly subtilc fluid, or etherial 



• Thore r.in not be a more fallacious means of estimating heat than by the touch. Thus, 

 in the onii^iary sfate of an apartment, at any season of the year, the objects which are in 

 it have all the samp tpmpcr.iture ; and • et to the touch tliey will fi-el warm and cold in 

 difforent degrees. The metallic objects will be the coldest ; stone and marble h'ss so ; 

 wood still IcKS ; and carpeting and woolen objects will feel warm. Now all these objects 

 are at exactly the same temperature, as ascurtuiucd by the thennumeter. 



