VOL. LI.] PHILOSOPHICAL TKANSACTIONS, 4 1 1 



of that colour, above 5 dwt. in the pair. When the white and the black stock- 

 ing were warmed at the fire, so as to be prepared for electricity, they usually lost 

 about a 20th part of their weight; so that in the course of the experiments he 

 rated the white at 174- ^wt. and the black at 1 oz. The scale, with the silk 

 lines that belonged to it, and the hook, was adjusted precisely to the weight of 

 1 oz. ; and as he commonly measured the strength of cohesion by fixing the 

 hook to the black stocking, and taking hold of the white, he had only to make 

 an allowance of 2 oz. more than the weights put into the scale, so as to take the 

 precise weight the stockings could raise by the power of cohesion. 



He measured this power two difierent ways ; the first whilst the one stocking 

 was still within the other ; 2dly, when separated, and the one afterwards applied 

 externally to the other. In the first of these cases, it may be thought that an 

 allowance should be made for the friction in pulling the stockings asunder ; l)ut 

 that appeared to be very inconsiderable ; for when those of the same colour were 

 put one within the other, and inverted, they dropped asunder of themseh^es ; 

 or if there was any entanglement about the heel, a little shaking disengaged and 

 separated them : however, if it should be thought proper, the allowance of an 

 ounce may be made, by deducting so much from the weight respectively found. 



In the experiments made to measure the force of electrical cohesion, he 

 always found it answerable to the degree of electricity at the time excited. 

 When the stockings have been but weakly electrified, he found them unable to 

 support the weight, the one of the other. When in a more powerful state of 

 electricity, they would raise, respectively, from 1 to 12 ounces and upwards ; 

 nay, once he found the cohesion so strong as to move 17 ounces, including the 

 scale and the black stocking. 



The greatest weight he had been able to raise by the force of electrical cohe- 

 sion, has been 17 ounces. Now the white stocking, which weighed but 174- 

 dwt. bore all this weight : in this case therefore it raised, by the strength of its 

 cohesion with the black, nearly 20 times its own weight. And if we consider 

 that the force applied to separate them, acted in a direction parallel to the sur- 

 faces, by which they cohered; and that when the surfaces are smooth, a force 

 acting in such direction, has much greater influence in separating bodies, by 

 making them slide gently over one another, than if those bodies were rigid, and 

 the force employed to separate them acted in a direction perpendicular to the 

 cohering surfaces ; when we consider this, it will be hard to determine how 

 great the strength of their cohesion may be. 



The force with which the black and the white stocking cohere, is not the 

 only thing remarkable in their junction. The solution of that cohesion, and 

 the different degrees of tenacity, according to different circumstances, afibrd 

 some curious observations. When the black and the white stocking are in co- 



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