148 



. And hence I suppose, that the weiglit of the atmo- 

 sphere is wholly inefficient, in keeping the mirror and 

 polisher in mutual coherence, when any liquor of per- 

 fect fluidity is between them; and that the force of co- 

 hesion acts alone to this effect. Accordingly, it is found, 

 tliat, when the polisher is so much wetted with water, 

 that there is formed a continuous plate of this fluid be- 

 tween it and the mirror, an additional force, sufficient 

 to squeeze out the water interposed, becomes requisite 

 to bring the surfaces into actual contact, and to produce 

 so much friction between them, as will serve to wear 

 down and polish the metal; which process will be found, 

 in these circumstances, to advance very slowly and irre- 

 gularly. And, on the contrary, when so little water is 

 applied to the jx)lisher, that it is only made damp, and 

 scarce wetted, (i. e. when there is not a continuous body 

 of liquid interposed between it and the mirror,) then its 

 contact with the metal will be so intimate and strong, 

 that the latter will pohsh very quickly. For then their 

 surfaces approach within the sphere of the attraction of 

 cohesion: insomuch that, if all moisture were suffered to 

 evaporate, the mirror and polisher would cohere so firmly, 

 as not .to permit any friction, or even a separation of 

 their surfaces, and the polisher v/ould be destroyed; for 

 then the weight of the atmosphere, also, would be 



superadded, 



the attraction extends, directly in right lines, to a distance from the sides of 

 the pipe, the coniposition of their forces ought to make the drop ascend, 

 ,tind spread itself in its course, as it happens in fact. 



