186 Prof. Draper on Capillary Attraction, 



known laws of electricity they mist therefore attract one an- 

 other. 



Is it philosopiiical to assume the existence of a new force 

 when there is one so palpably efficient at hand? 



(2.) If a plate of glass, hanging from one of the arms of a 

 balance, is lowered on the surface of some mercury in an 

 earthen cup, adhesion takes place; and it requires a consider- 

 able weight to be added on the other arm before the glass can 

 be separated from the mercury. This is a phaenomenon of 

 capillary attraction. 



But on trying, as before, with an electroscope, the glass is 

 found positive; and though the mercury is unelectrified, we 

 see obviously that its electricity has escaped into the earth. 

 And that this is true may be shown by putting the mercury 

 into a glass cup, or otherwise insulating it ; then the glass is 

 positive and the mercury negative ; they therefore ought to at- 

 tract each other. 



(3.) Two lead bullets pressed together adhere, — I presume 

 for the same reason that two pieces of glass adhere. On put- 

 ting them apart no electric excitement is discoverable, owing 

 to their conducting power *. 



(4.) When melted sulphur is allowed to cool in a conical 

 glass vessel, it adheres thereto. On forcibly pulling it out, 

 the glass is found to be positive and the sulphur negative; 

 they ought therefore to attract. 



1 might add other instances. These probably are sufficient 

 to communicate the idea in question. 



In all these cases the conducting power of the surfaces em- 

 ployed determines the apparent electric development; and in 

 those instances in which electric excitement cannot be detected 

 the reason is obvious. 



If a plate of polished iron is laid on a mercurial surface, ad- 

 hesion takes place, as in the case of glass; but on examining 

 the iron and mercury, no electric development appears, or, at 

 all events, the traces are very feeble. It could not, however, be 

 otherwise, for, owing to the conducting power of the surfaces 

 employed, a discharge from the one to the other must take 

 •place in the act of separation, and all electric pha^nomena cease. 



If a plate of glass be placed upon some water, it adheres 

 thereto by capillary attraction ; but on examining the glass 

 and water at the electroscope, neither of them indicates excite- 

 ment. And the reason is plain ; for the separation of the 

 glass from the water is only apparent. Its under surface is 

 wetted by a film of the liquid, and we have in reality only 



* What takes place if each bullet is insulated, takir.g care that there be 

 no difference of mechanical condition between them? — Edit. 



