346 CAPILLARY ATTRACTION, ETC. [MEMOIR XXVI. 



mutual attraction of a solid and liquid amount to less 

 than half the cohesion of the latter, the liquid will be 

 depressed in a capillary tube made of the solid ; if it be 

 equal to half, the liquid will stand level in the tube ; if 

 it exceed half, the liquid will rise. 



I published a paper in the Journal of the Franklin 

 Institute of Philadelphia for September, 1834, its object 

 being to show that the adhesion of surfaces, whether 

 solid or liquid, to each other, and the rise or depression 

 of liquids in capillary tubes, are strictly electrical phe- 

 nomena. 



When a glass plate is laid on the surface of quicksil- 

 ver, a considerable force is required to separate them. 

 On the separation being made, if the substances be ex- 

 amined by the electroscope, the glass will be found to be 

 electrified positively, the mercury negatively. Their at- 

 traction or adhesion is, therefore, a necessary electrical 

 result**- So intense is this electrical development that if 

 during the act of separation the mercury be in connec- 

 tion with a gold-leaf electroscope, the 

 gold leaves are commonly torn asun- 

 der. In Fig. 68, a a is a glass dish 

 containing mercury, c the glass plate, 

 - 68 - d the gold-leaf electroscope. 



In like manner, if some melted sulphur be poured into 

 a conical glass and permitted to solidify, on making the 

 separation the interior of the glass and the solid sulphur 

 cone will be found to be in opposite electrical states. 

 And the same occurs when surfaces of various kinds are 

 parted from each other. There ought, therefore, 

 to be adhesion. In Fig. 69, a a is the conical 

 glass, b the solidified sulphur, with handle for 

 its removal attached. 

 pig. 69. ]g ut ^ a g} ass plate be laid on a surface of 



water, there is no apparent development of electricity on 



