Oct. 9, 1885.] 



KNOWLEDGE ♦ 



311 



fusing the glass, the tube may bo plugged with a small 

 piece of dry wood or with a little plaster of Pari.s, and 

 then well coated with shellac; or, instead of either of 

 these, a stout test-tube may be employed, inverting it and 

 cementing the open end. It only remains now to coat 

 the under surface of A B with shellac varnish and the 

 apparatus is complete. With it many interesting and 

 instructive experiments can be performed. 



Ex. CXIII. A more elaborate, but in some cases more 

 useful form of condensing electroscope is illustrated in 

 Fig. 68, where CDEF is a wooden base about three- 

 quarters of an inch thick, six inches wide, and fifteen or 

 eighteen inches long. L is our electroscope (Fig. 61), 

 W W, the wire bent so that the plate A becomes vertical 

 instead of horizontal. B is the condensing plate illus- 

 trated in Fig. 67, a piece of quarter inch glass rod being 

 used instead of the piece of tubing GG. The rod is bent 

 similarly to W, and the lower end fastened by plaster of 

 Paris into a foot made by soldering a piece of brass tubing 

 on to a piece of brass, K, which slides over the two strips 

 of brass HH and LL, screwed along the middle of the 

 base, the strips being half an inch wide and long 

 enough to reach from within an inch or so of the 

 electroscope to the opposite end F D of th i base ; they 

 need not be more than a sixteenth of an inch thick ; they 

 should be a quarter of an inch apart ; but before being 



fixed, the wood separating them should be cut out with 

 a chisel and saw, a slot being thereby made a quarter 

 of an inch wide and equal in length to the brass strips. 

 Similar strips should also be screwed on to the correspond- 

 ing portion of the under side of the base. The foot-piece, 

 K, has to support B and the glass rod, and must also offer 

 facilities for changing the distance between the plate A 

 and B. To do this satisfactorily, K should present a ver- 

 tical section, as shown in Fig. 69. This may be easily 

 made. Cut two pieces of sheet brsiss, an eighth of an inch 

 thick and measuring three-quarters of an inch wide by 

 an inch long. These form the upper and lower pieces, A B 

 and D C, which slide over H 11, L L, and the correspond- 

 ing underneath pieces rospectivtdy. C is a piece of brass 

 a quarter of an inchtliick, an in.^h long, and sevon-oi-hths 

 of an inch wide, the width being just a tritle in excess of 

 the distance between the upper surfaces of the strips 

 H H L L, and the lower surfaces of the strips beneath. 



A B and D E, being screwed or soldered on to C, a very 

 ettioient foot, K, is at once provided and the movable 

 plate, B, can be easily placed at any distance from A, 

 within the range of the instrument. The foot might 

 also be made from a solid piece of brass, filing out the 

 necessary portions. When it is desired to connect B to 

 earth, the back surface may be touched with the finger, 

 or a piece of loose chain (Ex. VIII.) may be passed round 

 the piece of brass tubing into which the upper end of G 

 is cemented. It would be as well to coat G G with shellac 

 varnish. 



Ex. CXIV. A makeshift which I have occasionally 

 resorted to with advantage when hard up for an electro- 

 scope, and when the necessary materials are not to hand, 



Fig. 69. 



Fig. 70. 



is illustrated in Fig. 70. An ordinary wooden retort 

 stand is used, or (as is here shown) a wooden base A is 

 provided with a wooden rod B ; two pieces of wood are 

 screwed together on opposite sides of the rod, so as to 

 clamp it securely, and at the same time to hold in position 

 at C a piece of well-insulated (gutta-percha covered) 

 wire D E bared at the extremities, the upper end D being 

 bent in to a loop so as to prevent the extremity acting 

 as a point and discharging any electricity produced in 

 the instrument. The lower end E is bent at right angles, 

 the extreme point being turned back, and a gold or 

 Dutch-metal leaf hung over the wire so that the two 

 pendant parts are of equal length. Any open-mouthed 

 jar, such as the receiver of an air-pump, a pickle-bottle, 

 &c., placed on the base and the leaves suspended within 

 it completes the apparatus, which for temporary purposes 

 will do all that can be fairly expected of it. 



There are very many interesting and instructive ex- 

 periments which may be performed with the electroscope: 

 some of them I liave already dealt with ; those pertaining 

 to the condensing form of the apparatus should, in a 

 measure, su-'cst" themselves. In the main, they turn 

 on flic .[ucsti..!. . f induction, and it is to be hoped that 

 with the- :ip|. 11 iiii^ so far constructed, the Young Elec- 

 triciiiii will ri-<- ni iny a pleasant hour during the fast- 



The destruction of Flood Rock, near Hell G.itc, the preparations 

 for which were detailed in a recent issue of Knowledge, was to 

 h.ive been effected yesterday, but, owing, it is said, to slight imper- 

 fections in the insulation of wires, used to complete the electrical 

 firing circuit, the explosion has been postponed untU Saturday. 



