ELECTRICITY. 



525 





Practical plate to the conducting gilt surface on each side of it, 

 Electricity- and likewise with the size of the apparatus. 



SECT. IV. Cuthbcrlson's Condenser. 



Cuthbert- A VERTICAL section of this condenser is shewn in 

 on's con- p late CCXLIX. Fig. 17, where a and b are two Hat 

 and round brass plates, about six inches in diameter, 

 am ] screwe d tightly into the brass balls c, d. The ball 

 d is fixed to the top of a brass pillar e, which has a 

 joint at its lower extremity. The ball c is placed upon 

 a glass pillar firmly fixed into the wooden box : The 

 plate 6 can therefore be thrown back into the dotted 

 position shewn in the Figure. The insulated receiving 

 plate a, being connected with a wire to the body whose 

 electricity is to be condensed, remains in this state for 

 some time. The wire is then removed. The plate b is 

 thrown back into the dotted position, and the plate a 

 is presented to an electrometer, as formerly. 



SECT. V. Condensing Electrometer. 



Condensing THIS instrument, represented in Plate CCXLIX. 



ome " Fig. 18, is nothing more than the preceding condenser 



applied to an electrometer, the plate a of the conden- 



Fig. 18. ger being fixed to the cap of the electrometer instead 

 of the insulating stand c. When the plate a has re- 

 ceived the electricity from the electrified body, the 

 plate B is then drawn Iwck round the joint h, and the 

 electrometer instantly .indicates the condensed electri- 

 city. 



In order to increase the effect, Cuthbertson's con- 

 denser is sometimes used along with this instrument, 

 the lixed plate of the former being connected with the 

 fixed plate of the latter by a small brass pin. 



SECT. VI. Simple Condenser proposed by Mr Singer. 



Simplecon- MR SIN<;ER has proposed to construct a very simple 



denser pro- condenser, by placing three small spots of sealing wax, 



p-o.l ] go as to form a triangle on the lower surface of the 



Singer. ,,pp er conductor of the electrophorus. These spots of 



wax serve as short insulating legs, by which the plate 



may be supported at the distance of about the twelfth 



of an inch from the surface of a smooth and even ta- 



ble. The plate is then connected, as formerly, with 



the electrified body, and, after some time, the connect- 



ing wire is removed ; and the plate, when raised from 



the table, will exhibit the condensed electricity. 



SECT. VII. Read's Condenser. 



Head's con- Ijj this instrument, the fixed plate is placed hori- 

 zontally on a vertical insulated stand, and the move- 

 able plate is separated from it by turning a screw nut, 

 and allowing it to descend to the bottom of the stand. 



SECT. VIII. Nicholson's Spinning Condenser. 



Nicholson's A VERTICAL section of this ingenious instrument is 



spinning represented in Plate CCXLIX. Fig. 1<), where A is a 

 oonUcnser. . < i P . 



metallic vase, having a long steel axis, which passes 



Fig. 19. through a hole in the stand H at K, and rests with 

 its pointed end upon an adjustable socket at C. The 

 two shaded plates 1) and K are circular, and are made 

 of glass, being nearly 1 ,J inch in diameter, and T : . tli-, 

 of an inch thick. The plate D is fixed to the vase A, 

 and resolves along with it, while the plate II is fixed 

 to the stand. Two metallic hooks F, G, are cemented 



opposite to eacli other, into holes drilled in the edge of Practical 

 the plate F' ; and into the upper plate are cemented two Electricity^ 

 small tails of the fine flattened wire used in making sil- xi^hoisoiT's 

 ver lace. These tails are bent down, as shewn in the condenser. 

 Figure, so as to strike the hooks F, G during the revo- 

 lution, but so as to be free from the rest of the appara- 

 tus. By means of the screw at C, the distance between 

 the glass plates D, E may be increased or diminished. 

 The two contiguous faces of the glass plates are coated, 

 as shewn in Fig. 20. Each of the tails communicates 

 with the tinfoil coating of the plate D, and the hook F PI-ATE 

 with that of the plate E ; but the other hook G is com- 

 pletely insulated, and is intended to communicate only 

 with the electrified body. The instrument being thus 

 constructed, the moveable part of it, viz. the plate 1), 

 and all above it and the steel axis, is set a spinning by 

 the action of the finger and thumb upon the top T. 

 One of the tails will strike the hook G, connected 

 with the electrified body, and wHl receive and commu- 

 nicate to the coating of the plate D some of its electri- 

 city. At the end of half a revolution, the tail touches 

 the hook F, and electrifies it along with the upper coat- 

 ing, and the lower coating on the side of F. The tail 

 proceeds, collecting more electricity from the hook G, 

 and again deposits it at F, till there is so much conden- 

 sed as is requisite to produce a divergency in the pith 

 ball electrometer suspended at F. Mr Nicholson con- 

 structed an instrument of this kind five inches high, 

 and found it capable of condensing very small degrees 

 of electricity. See Nicholson's Journal, April 1797. 



For an account of other condensers, see Hemmer's 

 Condenser in Gren's Journal th'r Pltytik, vol. ii. part ii. 

 p. '210. Dumotiez's Condenser in Hozier's Journal, 

 xxxi. p. 441. Weber's Glass Condenser in Gilbert's 

 Annalen, xi. p. 3H. Wilson's Condenser, Doubler, and 

 Multiplier, in Nicholson's Journal, vol. ix. p. 19. 



CHAP. III. 

 On Instruments for Doubling Electricity. 



THE instruments called Doublert, are those which On instru- 

 are constructed in such a manner, that very small mcnts for 

 quantities of electricity may be continually doubled, doubling 

 till it becomes perceptible by the common electrome- elcctrlcn y' 

 ter. The first instrument of this kind was invented by 

 the Rev. Abraham Bennet. 



SECT. I. Description of Bennet' 's Douller. 



Tins instrument consists of two brass plates, which Bennet's 

 we shall call A and B. The plate A has an insula- doubler. 

 ting handle fixed in its centre, while the plate B has a 

 similar handle fixed in its circumference. Excepting 

 the upper side of A, all the sides of these plates are 

 varnished. The third plate C is a plate of brass var- 

 nished on its upper side, and laid upon Bennet's gold- 

 leaf electrometer. 



The body, whose electricity is to be doubled, is ap- 

 plied to the under side of the plate C, which lies upon 

 the electrometer, while B is touched with a finger of 

 the other hand, and then removing the coinnninieation 

 with the electrified body, B is lifted up by its insula- 

 ting handle ; and if the electricity is not now sensible 

 by the electrometer, A is placed, l>y means of its insu- 

 lating handle, upon B, thus elevated ; then touching 

 A, by stretching a finger over the juncture of its insu- 

 lating handle, and again withdrawing the finger, A U 

 1 



