KINETIC THEORIES OF GRAVITATION. 243 



transparent bodies, wo know that ponderable matter is not alone in 

 the universe; its particles swim as it were in a kind of fluid medium. 

 If this fluid be not the unique cause of all the observed facts, it must at 

 least modify them, diffuse their action, and complicate their laws. It is 

 then no longer possible to attain a rational and complete explanation of 

 the phenomena of physical nature, without recognizing the intervention 

 of this agent, whose presence is so inevitable. It is scarcely to be 

 doubted that in this intervention, sagaciously investigated, will be found 

 the secret or the true cause of the effects which are attributed to heat, 

 to electricity, to magnetism, to universal attraction, to cohesion, to 

 chemical affinities ; for all these mysterious and incomprehensible agen- 

 cies are at bottom but co-ordinating hypotheses, — useful without doul)t 

 to our existing ignorance, but which the i)rogress of true science will 

 complete by dethroning."* 



These passages are less notable for any j)recise hypothesis as to the 

 cause of gravitation than for their earnest unformulated faith in the 

 mechanical agencies of the tether as the fountain head of all force. 



A very striking illustration of the author's realizing sense of the 

 retherial presence occurs in a memoir communicated by him to the 

 Academy of Sciences about ten years before this time, or in 184:2; in 

 which, discussing the difference between the determination by Gay- 

 Lussac of the co-efficient of gaseous dilatation, and that made by End- 

 berg and verified by Regnault twenty-five years later. Lame made the 

 somewhat startling announcement that the observed difference indicated 

 an increasing ajther- pressure on terrestrial matter! "The difference 

 between these results is explained by admitting that the pressure of the 

 sether has undergone on the earth in a quarter of a century an aug- 

 mentation equal to a pressure of eight or nine tenths of a millimetre of 

 the mercurial column." t 



Waterston. 1858. 



In an essay "On the integral of gravitation, and its consequents with 

 reference to the measure and transfer, or commuTiication of force, by J. 

 J. Waterston," of Edinburgh, published in the Philosophical Magazine, 

 the writer commences with the general consideration : "Modern ideas 

 with relation to heat and the active condition of the molecular element 

 naturally incline us to estimate every force with regard to its work-pro- 

 ducing capacity. In the following paper I have considered gravitation 

 under this aspect, and in doing so, have been led to discuss some points 

 relating to dynamical sequence in the abstract." 



After referring to the fact that neither Kewton nor Laplace recog- 

 nized the principle of the conservation of Ibrce in their grand researches, 

 Waterstou continues : " Even at the present day, mathematicians have 

 been so long accustomed to and brought up in the statical method of 



* Loco cilat., sec. 134, pp. 3;>4, 33.3. 



t Comptcs Bendus, January 3, 1S4-2, vol. xiv, p. 37. 



