ALL MATTER, PONDERABLE AND lilPONDERAELE. 287 



walls of tlie observatory of Milan with very tlelicate instruinents, found thorn to 

 be subject to certain periodical and variable oscillations due to the action of the 

 sun. 'i\ibl)roni made the observation on a church of Paris, and to the same 

 cause is attributed the periodical uiovenient which Vicat observed in the arches 

 of the bridge of Souillae. 



[Professor Ilorsford has found that the top of the high tower which constitutes 

 the Bunker Hill monument, near Boston, inclines towards the west in the morning, 

 towards the north at midday, and towards the cast in the afternoon. These 

 movements are evidently due to the esjianding influence of the sun as it waiins 

 in succession the different sides of the structure. A similar but more marked 

 eflfect is produced on the dome of the Capitol at Washington, as indicated l)y the 

 apparent motion of the bob of a long plumT)-line fastened to the under side of 

 the roof of the rotunda and extending to the pavement beneath. This bob de- 

 scribes daily an elipsoidal curve, of Avhich the longer diameter is four or five 

 inches in length. 13y molecular actions of this kind, perpetually continued, time, 

 " the slow but sure destroyer," levels with the ground the loftiest monuments of 

 human pride. — J. 11.] 



But in what consists the mode of action of heat? In order to advance one 

 step in the solution of the question, it is necessary to recall the fact that in every 

 instance where there is a consiunption of mechanical labor there is a production 

 of heat. Attrition, compression, torsion, are each an expenditure of labor, and 

 give rise to heat. A band of caoutchouc suddenly stretched grows wami ; a 

 . strip fixed in a vice by one of its extremities, while the free extremity is made to 

 oscillate, becomes hot at the i)oint where it is fixed, that is to say, at the very 

 point at which the brisk force is annihilated. And, vice versa, when heat is 

 consumed labor is created ; a gas, in dilating, presses a piston and becomes colder ; 

 tlie same effect ensues when vapor expands. The band of caoutchouc, which 

 developed heat when suddenly stretched, creates labor and grows cool when we 

 abandon it to its previous contraction. 



When we are producing a vacuum under a bell glass, the internal air, through 

 its elasticity, ])resses the strata near the channel of evacuation ; thus labor is 

 generated, and the thermometer will be seen, in effect, to indicate a lowering of 

 temperature. If we now pe:^nit the external air to re-enter, it will compress the 

 air which has remained in the bell, and will lose the movement bv which it was 

 animati'd. In this exjHJriment, then, there is an expenditure of labor; hence, the 

 thermometer will be found to indicate an elevation of temperature. We have 

 been led by careful experiments to the following princijjle: ''When equal 

 quantities of mechanical labor are ])roduced by causes purely thermic, there is a 

 disappearance of equal (quantities of heat, whatever be the manner of operating ; 

 recijjrocally there is a ])roduction of ecpial (piantities of heat whenever equal 

 quantities of mechanical la])or are trausiurmed into effects purely molecular." TIkj 

 constancy of the relation l)et\veen the labor jn'oduced and the labor consumed, 

 whatever be the body which serves as a vehicle for this transformation, has been 

 proved by the experiments of Grove, of Joule, of Laboidaye, and other savants. 

 We are led to conclude from this that heat is ncjthing else than an active molecular 

 force. 



How can we do otherwise than admit that this singular transmutation of action, 

 this surprising transformation of force, depends on vibrations of the molecules of 

 heated bodies, capable of {)roducing in the ether corresponding imdulalious, which 

 are cajjalde in their turn of causing vibrations in the molecules of the bodies on 

 which they fall? Light and heat are inodilications of the same mechanical 

 principle; this, the capital experiments of Melloni have proved. These experi- 

 ments have led to the following unforseen results: ''That a luminous source 

 (the sun, the flame of a hunp) emits at the same time dillerent si)ecies of calorilic 

 rays, distinguishable from one another by the greater or less facility with which 

 they traverse certain diathermic substances." We now know that these calorific 



