mere CorltdSi of condii5iiri^ Suhjlances. 297 



experiments which may be made with this apparatus or chain 

 of cups much more eafilv, and in a manner more evident^ 

 and which, if I may be allowed the expreflion, fpeak more 

 to the eyes than thofe with the columnar apparatus. 1 fhall 

 therefore forbear from dcfcribing a great number of thefe ex- 

 periments, which may be eafily guefled,' and fliall relate only 

 a itw which are no lefs inftruilive than an)ufing. 



Let three twenties of thefe tumblers be ranged, and con- 

 nedled with each other by metallic arcs, but in fuch a man- 

 ner, that, for the firft twenty, thefe arcs fliall be turned in 

 the fame direction ; for example, the arm of filver turned to 

 the left, and the arm of zinc to ihe right ; and fbr the fecond 

 twenty in a contrary direftion, that is to fay, the zinc to the 

 left, and the filver to the right : in the laft place, for the third 

 twenty, the filver to the left, as is the cafe in regard to the 

 firft. When every thing; is thus arranged, immerfe one 

 finger in the water of the fird tumbler, and, with the plate 

 grafped in the other hand, as above diretled, touch the firft 

 metallic arc (that which joins the firft tumbler to the 

 fecond), then the other arc which joins the fecond and third 

 tumbler, and fo on, in fucceflion, till you have touched theni 

 all. If the water be very fait and luke-warm, and the Ada 

 of the hands well moiftened and foftened^ you will already 

 begin to feel a fliglit ihock in the finger \Vhen yoU have 

 touched the fourth or fifth arc (I have experienced it fome- 

 times very diftiniStly by touching the third), and by fuccef- 

 fivtly proceeding to the fixlh and thefeventh, &c. the (hock^ 

 will gradually incrcafe in force to the twentieth arc, that is 

 to fay, to the laft of thofe turned in the fame direction ; but 

 by proceeding onwards to the 2lft, 22d, 23d, or ift, 2d, 3d, 

 of the fecond twenty, in which they are all turned in a con- 

 trary diredcion, the (liocks will each time become weaker, fo 

 that at the 36th or 37th, they will be imperceptible, and be 

 entirely null at the 40th, beyond which (and beginning the 

 third twenty, oppof(2d to the fecond and analogous to the 

 firft,) the fliocks will be imperceptible to the 44lh or 45tli 

 arc -, but ihcv will begin to become fenfible, and to increafe 

 gradually,, in proportion as you advance to the 60th, where 



Vol. VI {. Qq they 



