515 PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



and light phenomena must have a much more intense character than 

 could be derived from any assumed combustions and chemical pro- 

 cesses, so that the spectral phenomena of the sun are in nowise contra- 

 dictory, but rather in accordance with the above suppositions. 



Although the heat produced by combustion and chemical combina- 

 tions is by no means sufficient to explain the retention of the sun's heat 

 (at least not according to terrestrial data and knowledge), these sources 

 are yet sufficiently striking and important to us, so that we are induced 

 to search for their primary cause ; and this all the more, as the heat 

 from combustion is to us in many cases indispensable. If a body falls by 

 reason of gravity, and its course downward is suddenly arrested, the 

 visible kinetic energy is changed to molecular motion or heat; in a sim- 

 ilar manner we suppose that the atoms of substances, acting upon each 

 other in non-measurable proximity and under favorable conditions, pre- 

 cipitate themselves with violence upon each other, by virtue of their 

 chemical attraction or relation, and so form the molecules of a new com- 

 position, wherein, by the violent shock, the suddenly arrested motion 

 is converted into the molecular motion termed heat. Just as the lifting 

 of a stone for the purpose of separating it from the giound requires work, 

 which it returns in an equal measure in its downfall, and which finally 

 turns into molecular motion or heat, so we require also energy, or in 

 many cases even heat itself, in the dissolution of chemical combinations. 

 Chemically separated substances may be compared to lifted weights or 

 tightened springs ; in short, they possess potential energy, which in the 

 chemical combination is again converted into kinetic energy, mostly heat. 

 This appears most strikingly in the chemical combination of substances 

 with oxygen, from which result the phenomena of light and heat, and 

 which is called combustion ; and from the heat thereby generated heat 

 was first measured. In all oxidations and, speaking more generally, in 

 every chemical combination, whether produced directly or indirectly, at 

 one time or at different periods, an equally large amount of heat is al- 

 ways produced for this combination. If, for instance, a weight -unit of 

 coal were first converted into carbonic oxide and this into carbonic acid, 

 just as much heat will have been developed in the end as if the coal had 

 been converted into carbonic acid directly. 



The oxidizable components of the blood in human and animal bodies 

 suffer a slow and gradual oxidation, whereby the human and animal 

 vital heat is produced. As the products of oxidation of the living 

 animal body are thrown off by respiration (carbonic acid, water, and 

 nitrogen), by perspiration (water, carbonic acid, and various combina- 

 tions), and in other ways, a compensation for these oxidized substances 

 becomes necessary. This compensation is secured by means of food, 

 which is always taken from either the animal or vegetable kingdom, 

 and must, on the whole, be oxidizable, because its components eventually 

 are oxidized in the animal blood; that is, they combine chemically with 

 the oxygen of the inhaled air. In animals a part of their heat is 



