I g EL'ffrieal InJ! rum flit. — Pnr:li/ig. 



The lower coating nean-ft to G is nude to communicate permanently with the (land H, 

 and confcquently with the earth. 



In tliis (Itii.uion, fuppofe the motion of fpinning to be given to the apparatus, and the ef- 

 fects will be thtfe : — One of the tails will Itrike the hook G, by which means the upper 

 coating annexed to that tail will adumc the eleflric (late of L by communication. But 

 this flate, on account of the proximity of the lower uninfulated plate to which it is, at that 

 inftant, dircdly oppofed, will be as much ftrongcr than that of L, as a charge exceeds fimple 

 eleftrization. The tail G with its plate or coating proceeds onward, and aftK;r half a revo- 

 lution arrives at the fituatlon to touch tlie hook V. The upper coating, the lower on the 

 fide of F, the hook F itfelf, and the t.iil V, mud then conftitute one jointly infulatcil 

 metallic mafs, in which no charge fubfifts, but which is fimply ele£lrified by the whole 

 charge received at G. And of this mafs the furfaces of the plates themfelves, conftituting 

 the eleftric well of Franklin, will throw out all their eleflricity to the hook and tail. But 

 the coating and its tail inftantly pafs round, leaxlng F eleflrified, and proceed to bring 

 another charge from G and depofit it as before. The balls at F are therefore very 

 fpeedlly made to diverge. It is fcarcely neccflary to remark, that the two upper coatings do 

 nothing more than double the fpeed of the operation ; one of the tails being employed in 

 collecting, while the other is depofiting: and that the gold leaf eledlrometer may be ad- 

 vantageouHy fubftituted for the cork-balls. 



The inftrument I caufed to be made was five inches high. The receiving fide G was 

 conneiSed with a coated jar of four fquare feet coating, and the giving fide F was con- 

 nected with Rennet's gold leaf electrometer. The eleCtrometer was rendered as ftrongly 

 pofitive as it was capable of being, and the jar was rendered negative, by giving it as 

 much of that power as was produced by drawing a common ftick of fealing-wax once 

 through the hand. In this ftate the jar was incapable of attracting the fineft thread. 

 The vafe was then made to fpin ; and the effeCt was, that the leaves of the eleCtrometer 

 firlt gradually collapfed, and then in the fame manner gradually opened, and (truck the 

 fides of the glafs of the eleCtrometer with negative eleCtricity. The experiment was ro 

 newed and repeated with every requifite variation. 



IV. 



Ohftrvations on the Art of Printing Books and Piece Goods by the ABion of Cylinders. 



'—— Experto credite. 



W E may conceive three ways of delineating figures, or writing. The firft and mod 

 ancient cjnfilts in making the traces fuccelDvely by a brufli, a pen, or other inftrument. 

 This is defign, painting, or writing. In the latter methods, either the whole or the 

 greater part of the figures are made by the aCtion or pre(rure of an original pattern 

 againft the material intended to be written or painted upon. It is the art of printing. 

 The colouring matter is either depofited from the face of prominent parts of the original 

 form, which is ufually called a block or type ; or elfe it is prelTed froai cavities cut in 

 the face of the original, which in thi^ cafe is Citlled an engraved plate. Mod books are 



pinted 



