ELECTRICITY OF METALS. 



43 



metals from contact. And this fuppofition was very much 

 ftrengthened, when, upon examination, I found that all who 

 have made experiments on this fubject have feparated the metals 

 from contact before thev examined them as to their electricity. 



If the contact of the two metals be the caufe of the electri- —determinable 

 cal figns, hi whole effect tKat one metal can have on another fj r f ace j t ° 

 wiil be communicated at the time of contact, however few the 

 points are that form Uie con ^ct/beca^fe both the metals being 

 conductors of electricity, if one pofTeffed a greater proportion 

 of it titan the other, a parr, will be communicated to the other 

 at. the time of contact, to form an equilibrium, and this wiil 

 be done as veil by a few points of contact as by a great many. 

 Bin if it is the feparating them from contact, that is the caufe 

 of the dyctrical fign, (he more exienlive the contact is the 

 more powerful will the figns be when the metals are feparated. 



To put this to the teft of experiment, I pierced apiece of Sieve of one 



thin meet copper full of fmall holes, juft big enough to permit ™ etal and filin S s 



\*. • . en- r . of another, 



to pats throug.i them two or three particles or filings of another 



meial al a time, fo that aim oft every particle muft be in con- 

 tact with the copper before i( can pafs through, and confe- 

 queritfy the lurface of contact be very great with a compara- 

 tive v fmall quantity of metal. 



1 lifted through this copper h'eve fome filings of zinc into a 

 tin pi ite laid on the cap of a gold leaf electrometer, and the . 

 gok leaves diverged near an inch with pofifive electricity* 

 when about half an ounce of filings had been fifted into it. 

 Encouraged by this fir iking refult, I procured heves and filings 

 ot different metals. The refults of the trials with them are 

 contained in the following table; where P ftands for pofitive 

 electricity, I\' fo negat've, and when it was not ftrong enough 

 to effect the electrometer, that is denoted by O. 



Refults of ex- 

 periments. 



Filings of 



Sifted thro 



ugh 



Effect. 



Copper 



Copper 



Tin 



Silver 



Zinc 



Lead 



o. 



N. ftrong 



P. ftrong 



N. 



Zinc 



Copper 



Tin 



Sii.er 



Zinc 



Lead 





P. ftrong 



O. 



P. ftrong 



P. exceeding weak 



O. 



