270 KINETIC THEORIES OF GRAVITATION. 



-pis iJtm absorbed from the aether, heat light and magnetism are produced 

 in the body as shown in the stars. " This cause being permanent, explains 

 without difficulty why the light and heat of the sun are constant "! A 

 body in motion is of course retarded by the relative differential of the 

 currents, although this retardation would be sensible only with very 

 light bodies. 



Considering secondly, the case of two bodies, (exterior to each other,) 

 the currents enfeebled by traversing the bodies would impinge less 

 strongly on the' mutually-facing sides of the two bodies than on their 

 exterior sides, thus producing an approach by the difference of impulse. 

 And lastly, in regard to weight, this is the result of the quantity of 

 motion communicated to a body by the shocks of the setherial atoms. 

 The two facts of experience, that the weight of a body remains invaria 

 ble whatever its position, and that all bodies fall with the same velocity 

 in a vacuum, prove that ponderable atoms are spherical, having an equal 

 superficial density in all directions, and that all ponderable atoms are 

 alike, or that there is ultimately but a single elementary substance.* 



BOISBAUDRAN. 1869. 



Another short paper, entitled a "Note on the Theory of Weight," was 

 presented to the Academy September 20, 1869, by M. Lecoq de Bois- 

 baudran, called forth by the previous communication of M. Leray. He 

 remarks: "Having been myself occupied on this question, I have the 

 honor to communicate to the Academy the actual state of my researches. 

 On certain points, and particularly on the explanation of the central, 

 heat of the stars, I am happy to agree with M. Leray ; on other points 

 my conclusions differ from his. I attribute to matter, whatever may be 

 its state of division, no other essential properties than those established 

 by experimental physics and mechanics. I designate as atoms the last 

 stage of division of matter. I admit that two bodies separated by an 

 absolute void cannot act on each other ; that action takes place only by 

 contact, the play of forces following the laws of ordinary mechanics. 

 If there existed but a single kind of atoms, the interchange of forces 

 occurring between equal masses, two atoms could not unite. Force and 

 matter would exist, but not attraction. There are then at least two 

 kinds of primordial atoms of different masses. The smaller may be 

 called aether ; the others, ponderable atoms." The writer then goes on 

 to say that a ponderable atom in the midst of a vibrating aether would 

 itself receive a vibration (though of less activity than that of the aether) 

 without being displaced in space, the portion of energy lost by the aether 

 being transformed into heat, etc. A second atom being placed near the 

 first, the aether vibrations would be feebler between the two than in ex- 

 terior space, which would result in approach. 



" I prefer the notion of vibrations of the aether to that of * equal cur- 

 rents crossing each other in all directions.' The attraction exerted on 



* Comptes Eendus, 6th September, lt;69, vol. Ixix, pp. GI6-6'20. 



