44*2 Mr. W. li. Browne on Action at a Distance* 



ot a wave in such a gas = — x the velocity of the gas-par- 



o 



tides. Since the velocity of waves in the aether is about 



180,000 miles per second, this would give the velocity of the 



panicles themselves = about 130,000 miles per second — a 



velocity immensely below what is required to account for the 



fact of non-resistance. But if the aether and the gravity-gas 



be different bodies, the particles of the latter must be colliding 



continually with those of the former, as they collide with the 



molecules of ordinary matter. How is it that no effects due 



to such collisions are observed ? It would seem likely that 



they would assume the shape of a diffused glow of light and 



heat, growing more and more intense as the translatory motion 



of the gravity-particles was turned into vibratory motion of 



the aether-particles. It is needless to say that nothing in the 



least resembling this takes place. 



"We will here leave the discussion of Le Sage's impact theory, 

 as explaining the particular case of gravitation, and go on to 

 inquire how the same, or any other impact theory, can explain 

 some other phenomena of the universe. We w T ill first take 

 those of cohesion. 



Cohesion. — To fix our ideas, let us take the case of a square 

 bar of good wrought iron or mild steel, 1 foot long and 1 square 

 inch in area. Then the following two facts, amongst others, 

 have to be accounted for: — 



(a) The extension of the bar as a w 7 hole (and therefore the 

 extension of the mean distance between the successive layers 

 of its molecules) by j^q o °^ ^ s length is sufficient to produce 

 between the successive sections of the bar a stress of tension 

 (taking the form of an attraction between the sections) of 

 about 15 tons, say 8000 times the attraction exercised by the 

 earth upon the whole bar when placed in contact with it. 



(/>) The contraction of the bar through the same relative 

 distance is sufficient to produce between the sections a stress 

 of compression (taking the form of a repulsion between the 

 sections) also of 15 tons or thereabouts. 



Can these two facts be explained on any of the three impact 

 theories, which we have shown to be the only possible ones ? 

 It seems almost sufficient to ask the question; but it may be 

 well to take them in order. 



(1) Can the facts be explained on the hypothesis of direct 

 contact between the molecules ? Were this true, it would be 

 impossible to produce any contraction of the bar without 

 forcing two solid bodies into the same space. It is obvious 

 that it will not do to suggest that the contraction may be in the 

 molecules themselves ; for then we have only to transfer the 

 inquiry to the particles composing those molecules. Are these 



