DOVE ON THE EI>ECTRICITY OF INDUCTION. 113 



an inch in width (Plate I. fig. 3), are coiled two spirals of cop- 

 per wire in the same direction, completely imbedded in shell- 

 lac, and surrounded on the outside with paper. Each of the 

 spirals forms 80 coils with 32 feet of wire. Of the wire-clamps 

 in which these "spirals terminate, a is connected with the inner, 

 and d with the outer coating of the insulated battery, after 

 this has received a constant charge by means of a unit jar. 

 As the clamps b, &c. are united by a cross-wire, the two spirals 

 a b and c d form together the connecting wire of the battery. 

 The induction- spirals, coiled in the same direction as the inner 

 ones which they are to enclose, are wound upon tubes of paste- 

 board, and hnbedded in shell-lac, each wire having a length 

 of 45 feet and 80 coils. The thickness of the wire of these 

 spirals is the same as that of the wires of the connecting 

 spirals, namely, half a line : both ends of each secondary spiral 

 are on the same side (in the front of the figure) ; the longer end 

 of each spiral, which is bent back (/3, 7), passes therefore along 

 the external paper covering, enclosed in a glass tube, which is 

 fixed by two silken bands, with the aid of small pieces of cork. 

 Of the four ends of these spirals, two, a and 7, are connected 

 by a cross-wire, whilst the others, /3 and S, either terminate in 

 handles, as is represented in the figure, or are connected by a 

 spiral containing an unmagnetized steel needle, by a galvano- 

 meter, an electro-magnet, an apparatus for decomposition, an 

 electric air thermometer, or one of Breguet's metallic thermo- 

 meters, an insulated preparation of the frog, a condenser, or 

 an apparatus consisting of points with an insulated disc of resin 

 between them, for the production of figures on the resin. Each 

 of the connecting spirals, a b and c d, rests with its surrounding 

 secondary spirals, «/S and 7 8, upon two glass feet | of an inch 

 in diameter, and well- covered with shell-lac ; these branch out at 



I the height of 8i inches into a fork composed of two glass rods, 



■ each of which is 3 inches in length, and these are fixed into brass 

 caps by cement, at a distance of li inch from each other at 

 the top, upon the vertical stems. Into the interior glass tubes 

 the metallic cylinders and bundles of wire which are to be com- 

 pared are introduced, as is shown in the figure, where the spiral 

 c d incloses a solid cylinder, and the spiral « A a bundle of wire 

 surrounded by a metallic tube. The apparatus was made by 



I M. Kleiner with his usual care. 



I I now proceed to the experiments themselves. 



, VOL. V. PART XVII. I 



