

E' ' 



17 



114 xlO 10 



20 



118 „ 



318 Mr. E. II. Hall on the note Action of 



Silver. 



Measurements have been made with four separate plates of 

 tins metal. The thickness of the strip was estimated in one 

 case by weighing, in the three others by measuring the elec- 

 trical resistance. I will give first the results obtained with 

 the thick strip. 



Silver-foil, No. 10. 



Length of strip when weighed =7*98 centims. 



Width „ ,, ' =rl-07 centim. 



Area, including projections . =9*23 square centims. 



Weight = -0474 grm. 



.-. Thickness (taking sp. gr. to 1 = . 000491 centim< 

 be 10-47) . . . . J 



With this plate, 



M. C. 



April 21st, 6580 kx tan 49 

 >) )) a » °* 



Mean . . = 1160 xl0 y 



Two of the other plates were prepared, not by fastening 

 silver-leaf to glass with shellac, but by depositing from a solu- 

 tion the silver directly upon the glass. The process made use 

 of for this purpose was Bottger's, as detailed in Silliman's 

 Journal for 1867. The two plates were cut from the same 

 piece of glass, after coating. 



Stiver Film A. 



Length between the contact blocks =6*05 centims. 



Width =2*46 centims. 



Electrical resistance, as measured . =1*45 ohm. 



Knowing that the contact-resistance must be quite a part of 

 this value, I endeavoured to determine its amount roughly in 

 the following manner: — Having obtained the above value, 

 1*45 ohm, and measured the distance between the blocks, I 

 shortened the strip by placing the blocks nearer together, then 

 measured the length and again determined the resistance of 

 the whole. This process was repeated, thus giving three 

 values of the resistance, corresponding to the three lengths of 

 the strip employed. From these values the contact-resistance 

 is readily determined, though of course very roughly. It ap- 

 peared to be equal to the resistance of about 2*7 centims. of 

 the strip itself; and therefore, in estimating the thickness of the 

 strip from the electrical resistance, the effective length of the 



