156 



ON THE IDENTITY OF LIGHT, HEAT, 



at the same time, but simply is described as filling the inter- 

 stices between these elementary particles. It is also as capa- 

 ble of transmission from one substance to another, as water 

 when poured from vessel to vessel. It is to a certain extent 

 capable of accumulation and retention, without renewal, like 

 other fluids in nature ; we find that the retention of these 

 latter is of very short duration if left to evaporate, uncovered 

 and unprotected, or in contact with leaky or porous sub- 

 stances. 



There is therefore reasonable ground for concluding, that, 

 as every known substance in nature is ntere or less porous to 

 the calorific fluid, if caloric could be as effectually sur- 

 rounded by substances incapable of its transmission as the 

 liquids in daily use can be, we should be able to preserve it 

 at any degree of intensity, and that without addition, for any 

 protracted period. 



But it is manifest that whatever may be the teaching of the 

 Schools with regard to the nature of caloric — they all practi- 

 cally denominate it not as a mere mode of action or the result 

 of motion among the particles of matter — but as a bond fide 

 and genuine substance, and as endowed with all the powers 

 and qualities usually attributed to real material existences. 



The facts that appear to me especially unanswerable, bearing 

 against modern theory are, that if one were to admit for the 

 sake of argument that caloric is generated by friction, why does 

 not the effect cease when the cause is discontinued? — why does 

 it not cease to exist when friction ceases f — or else, why is not 

 caloric daily and hourly accumulating ? How is it that when 

 by such heat generated we have kindled a fire, which might 

 also be admitted to depend for its development on motion of 

 a chemical nature occurring among its own particles, — how is 

 it that by this same fire, once produced, we can communicate 

 a certain degree of redness or white heat to a piece of iron or 

 other substance, without producing any motion among its 

 particles, and with this heated metal we can communicate 



