tlEPLECTlNG tELESCOPE. 49 



It is formed ; and no farther resistance arises to their disjunc- Argumentsand 

 , , . . , .... /♦,! n -J • i J inferences res- 



tion, than what is owing to the viscidity of the fluid interposed, pgcting the 



and to the force of cohesion ; which latter acts, in this case, process of po- 

 quite different from any external force of compression; and ^^ mg minors, 

 prevail?, as I apprehend, to a small distance from the surface, 

 diminishing in the ratio of some high power of that distance. * 



And hence I suppose, that the weight of the atmosphere is 

 wholly inefficient, in keeping the mirror and polisher in mutual 

 coherence, when any liquor of perfect fluidity is between them; 

 and that the force of cohesion acts alone to this effect. Ac- 

 cordingly, it is found, that, when the polisher is so much wet- 

 ted with water, that there is formed a continuous plate of this 

 fluid between it and the mirror, an additional force, suflicient 

 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 circumstan- 

 ces, to advance very slowly and irregularly. And, on the 

 contrary, when go little water is applied to the polisher, that 

 it is only made damp, and scarce wetted, (i. e. when there is 

 not a coutinuous 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 polish very quickly. For then their 

 surfaces approach within the sphere of the attraction of cohe- 

 sion : 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 would be destroyed; for then the weight of the atmos- 

 phere, also, would be superadded, when no fluid is interposed : 



* If it were supposed, that the force of cohesion is confined to 

 the surface of bodies, and acts only in the state of actual contact; 

 it would be hard to conceive, why a drop of liquor should ascend, 

 in a conical glass-pipe, whose narrow end was elevated : since 

 the drop ought, on this supposition, to be attracted as much by 

 the surface below, as by that above it: and its weight ought t(? 

 make it descend ; and there would be nothing to make it spread 

 beyond the space of contact which it occupies: whereas if the 

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

 sides of the pipe, the composition of their forces ought to make 

 the drop ascend, and spread itself in its course, as it happens ia 

 fact. 



Vol. XVI.— Jan- 1807. —Nq.SS. E 



