of the Approach and Recession of Bodies. 79 



phenomena, which, as they involve a general principle, I am 

 tempted to quote : — 



" ' The experimental results appear to me to point to the 

 following conclusions : — 



" 'Whenever an elastic medium is between two vibrating 

 bodies, or between a vibrating body and one at rest, and 

 when the vibrations are dispersed in consequence of their 

 impact on one or both of the bodies, the bodies will be urged 

 together. 



" ' The dispersion of a vibration produces a similar effect 

 to that produced by the dispersion of the air current in 

 Clement's* experiment, and, like the latter, the effect is due 

 to the pressure exerted by the medium, which is in a state 

 of higher mean tension on the side of the body furthest from 

 the origin of vibration than on the side towards it. 



" ' In mechanics — in nature there is no such thing as a 

 pulling force, though the term attraction may have been 

 used in the above to denote the tendency of bodies to 

 approach— the line of conclusions here indicated tends to 

 argue that there is no such thing as attraction in the sense 

 of a pulling force, and that two utterly isolated bodies 

 cannot influence one another. 



" '* If the getherial vibrations which are supposed to con- 

 stitute radiant heat resemble the serial vibi f ions which 

 constitute radiant sound, the heat which all b< Jes possess, 

 and which they are all supposed to radiate in exchange, will 

 cause all bodies to be urged towards one another." 'f 



"Clearly, then, we may have these rotations and approxima- 

 tions due either to currents or periodic vibrating impulses, 

 without the necessity of supposing either special properties 

 of attraction or the existence and exercise of any new force. 



" When a gaseous atmosphere is present, it seems to me 

 that the existence of currents adequate for producing the 

 phenomena of approach is an obvious fact ; and, when 

 moisture is present on solid surfaces, as in the case of the 

 bedewed glass shade, that the recession can result from its 

 evaporation. In short, that these two operating influences 

 are antagonistic to one another, and that we may have one 

 or the other effect, according as one or other of these 

 influencing causes is in the ascendant. 



* The experiment of Clement shows that when a continuously renewed 

 current of air passes between two parallel discs from the common axis 

 towards the circumference, the discs are urged together. 



f Proceedings Royal Society, vol. xix. p. 41. 



