THEORY OF COHESION. 177 



it is certain that in a philosophical sense, the 

 words heat and cold are only relative terms, 

 which indicate different proportions of the same 

 aethereal agent. 



It is because the attraction of caloric for solids 

 exceeds that of liquids, that their cohesion is 

 'greater than that of liquids. It is because the 

 attraction of mercury for caloric exceeds that of 

 water, that its particles are held together with a 

 greater force of cohesion. When reduced to the 

 temperature of 39, the attraction of mercury 

 for caloric is so far augmented that it assumes 

 the solid form : but the most important fact con- 

 nected with this change is, that it acquires a 

 corresponding power of attracting other bodies, 

 the temperature of which is higher. It was 

 before stated, (page 106,) that when the hand is 

 applied to frozen mercury, its caloric is rapidly 

 withdrawn. They are also held together with 

 great force, as iron is attracted by a powerful 

 magnet when charged with electro-caloric by a 

 voltaic battery. It is therefore highly probable, 

 that if the temperature of mercury were reduced 

 100, it would abstract from animal bodies their 

 vital heat with a force and rapidity resembling 

 an electric shock ; and that if it were possible 

 to reduce its temperature two thousand degrees 

 below zero, the force of its attraction for caloric 

 would surpass all means of computation ; while 



N 



