ON GALVANISM. 291" 



From thefe principles we fee, why the' apj^aiStusof Mr. Rltter's pile 

 RItter is better adapted to feparate thefe two kinds of a61Ion J^parate^the two 

 than any other. In the common pile the intenfity increafes*ftions. 

 with the number of pairs of metal, and balances therefiftance 

 arifing from thefe alternations; while in thefecondary pile the 

 intenfity of the two extremities can never furpafs that of the 

 primitive pile, and the refiftance produced by the alternations 

 is entirely employed in modifying the current of a given (Quan- 

 tity of eleftricity. 



In fine, if Volta's pile can thus change the fecondary pile But VoIta*s pile 

 of Ritter, this property is owing to its intenfity being ex- ^^^"'^ "ot charge 

 tremely weak, and as we may fay imperceptible. A niore^lj.^rjg-u' J^j.^ 

 powerful eledricity, fuch for example as that of the common net very weak. 

 eleftrical machine, would pafs through the apparatus com*, 

 pletely and not produce the fame effects. 



Though thefe deductions appear to us very natural, we of-T'^e^e deduc- 

 fer them only with extreme referve, and becaufe we think they vaTced'as^ce'r- 

 agree very well with the fads obferved by Mr. Ritter. tainties. 



The differences that exiil in the chemical a<5lion of common Caufes of dlf- 

 piles, in proportion to the fize of the plates, occur likewife in fj^^^^J^ \^^ 

 the fecondary piles. The arrangement of the pieces of pafte- 

 board, their thicknefs, the nature of the folulioh with which 

 they are wetted, and the order in which they are interpofed. It would be ufe- 

 as well as various other trifling circumfiances, inodify the ef- jl^^^^^g^J^"^ 

 fe6ts in a thoufand ways, which it would be both ufeful and its effeds. 

 curious to inveftigate, - «"''*5**^^ 



XL 



On Spedtacles; particularly the Perifcopic. In a Letter from 

 Mr. E. Walker. 



To Mr. NICHOLsdN. 



Lynn, March \9, 1804. 

 SIR, 



-t\LTHOUGH the improvements which have been made Spe^ades have 



in optics within the laft century, have been fuch as even to ex- "°^ ^^f"^ '"^* . 



r rt • /• XT '1 proved as' much 



ceed the expectations of a Newton, yet our ipedacles, the as other optical 



raoft ufeful of all optical inftruments, have remained for ages '"iftrumcnts. 



in the fame ftate of imperfeftion. Many alterations, it is true, 



U 2 have 



I 



