Experimental Researches on Gravitation. 489 



Characters of Newton s Law. — In its simplicity this law 

 seems the most perfect of the physical laws. Up to now 

 no influence of the nature of the medium has been detected 

 in the propagation of the attractive force between two 

 material masses. The researches of Austin and Thwing *, 

 Kleiner t, Laager {, Cremieu§, Erisman ||, and others 

 having in view the discovery of an action of that kind, 

 failed utterly. In consequence of Laager's experiment, in 

 which he studied the weight of a silver ball, covered with a 

 thick coat of lead, it may be thought that the lack of effect 

 has been until now verified up to the approximation of about 

 5.10 -5 . The result was obviously a confirmation of the 

 exactitude of Newton's Law. 



Doubts on the exactitude of Newton's Laic. — It does not 

 seem right to me to deduce from an experiment, like Laager's 

 for instance, that what has been verified in the Laboratory, 

 might repeat itself with the same appearance, even in 

 astronomical cases. Hence it would not be right to deduce 

 therefrom that the mass of the silver ball would appear the 

 same if in the centre of the earth, or in the centre of the sun 

 (333,000 times the mass of the earth). 



Let us admit as an hypothesis, that the mass may appear 

 smaller if surrounded by other masses, that is, that there is 

 a diminution of the force of gravitation on account of its 

 propagation across a material medium. This diminution 

 might be owing to a property of the material medium, to be 

 compared with electric or magnetic permeability, or to the 

 progressive absorption of the force. In the first cnse, if the- 

 analogy with the electrical and magnetical phenomena could 

 be proved, small thicknesses of the medium would be 

 sufficient to allow of the verification of the hypothetical 

 permeability of gravitation ; this has not been done in the 

 experiments known up to now. In the second case the 

 absorption would occur for very great thicknesses of medium, 

 and therefore escape the researches of the laboratory, and 

 yet manifest itself in the celestial bodies. In consequence, 

 this second hypothesis of absorption seems more probable, 

 and its conception would be more easy, if the force of 

 gravitation could be explained by a kind of energical flux, 

 continually emanating from ponderable matter. This flux 



* Phys. Rev. v. (1897). 

 t Arch. sc. phys. et nut. xx. p. 420 (1905). 

 + Dissert. Zurich (1904). 



§ C. R. cxl. p. 80 (1905) : cxli. pp. 653, 713 (1905) ; cxliii. p. 887 

 (1906). 



IJ Vierteljahrschr. liii. p. 157 (1908). 



Phil. Maq. S. 6. Vol. 39. No. 233. May 1920. 2 K 



