French National Institute. 173 



The water in the reservoir always acquires the same degree 

 of heat nearly m the same time. Hence the power of the 

 rays to produce heat is always proportional to their quantity 

 whether they are concentrated or not ; or, what amounts 

 to the same thing, the heat produced is proportional to the 

 light absorbed. 



It has long been believed that the heat of the earth does 

 not all come from the sun, but that it is indebted for a great 

 part of it to some focus concealed in its interior part ; this 

 is the old hypothesis of Descartes, which Buftou after- 

 wards made the basis of other systems, M. Peron, sent 

 by the Institute, as naturalist, wilh captain Baudin during 

 his voyage of discovery, has made an extensive series of 

 researches to ascertain the truth of this fact. He examined 

 with an ingenious apparatus the temperature of the sea at 

 different depths, and he every where found that it is colder 

 the greater the depth. This result, agreeable to that bcforo- 

 obtamed by English navigators in other seas than those 

 traversed by M. Peron, seems to destroy entirely the idea 

 of a central fire. It is even probable that the deepest abysses 

 «f the sea are always frozen, even under the equator, in the 

 same manner as the summits of the highest mountains *. 



M. Biot has made a curious experiment in regard to the 

 heat forced from bodies by compression. Oxygen and hy- 

 drogen gas, when merely mixed at the ordinary degree of 

 the pressure of ihe atmosphere, have need, in order to com- 

 bine, of the action of the electric spark. When \mt. toge- 

 ther in a condensing machine they combined merely by the 

 heat which was disengaged, and abandoned one so consi- 

 derable at the time of their combination that the machine 

 burst every time the experiment was repeated f. 



Common air, the medium in which not only the greater 

 part of the phtenomcna of chemistry but those also of or- 

 ganic life take place, cannot be studied too carefully by 

 philosophers. Its degree of purity, that is to say, tl>e pro- 

 portion of oxvgcn it contains, is one of the most important 

 points that can be examined. Messrs. Humboldt and Gay- 

 Lussac have compared the diflerent means hitherto invented 

 for meastiring this proportion, and have shown that the 

 best of all is that of Volla, which consists in burning hy- 

 drogen gas. A hundred parts in voUudc of oxygen are ne- 



• This reasoning is very inconclusive. For, if the earth contains Iic;it that 

 ioet not come from the sun, the water which it warnis must ascend to tlie 

 »urface, being displaced by tliat \s'l)ich is colder, and consequently more 

 dense. — Edit. 



t .See Philosophical Magazine, voL xxi. p. Mi'.'.- 



cessary 



