156 



KNOWLEDGE 



[March 1, 1886, 



For the purpose of making the connectious, procure a 

 couple of copper or brass washers (like those used in 

 making the handle) about five-eighths or half an inch in 

 diameter, and furnish it with a hole (A, Fig. 1) about an 

 eighth of an inch in diameter. Drill two other holes, 

 B C, large enough to allow stout brass pins (or nails) to 

 pass through. Round oil, with a file, any asperities, and 

 then pin one of the pieces of metal on the wooden cylinder 

 carrying the rubber, jilacing it in the centre of the outer 

 side or that side remote from the gla.s.s. A gimlet or bradawl 

 .should next be used to make a hole in tiie wood corres- 

 ponding with the hole A (in Fig. 1). Into this hole drive 

 lightly a short brass-headed nail (such as is frequently 

 used for hanging pictures). It would be an improve- 

 ment to sink the brass washer or collar into the wood by 

 making a shallow hole therein with a brace and centre or 

 twist bit of the necessary size. If the washer fails to 

 make contact with the foil coating of the wooden cylinder, 

 a piece of tin-foil should be pasted on so as to preserve 

 the electric continuity. 



3' Li 



Kisr. 1. 



Fig. 



Fig. .■!. 



The other washer should be similarly fixed on the outer 

 side of the prime conductor, and should bo likewise fur- 

 nished with some such article as a brass-headed nail for 

 connecting purposes. The nail should not, however, be 

 fitted tightly, as it will often be found advantageous to 

 remove it and substitute a piece of stout iron or other 

 wire, provided at one end with a metallic or metal-coated 

 ball. A very efiicient substitute for a metal ball is a 

 wooden one, painted with gold-size and rolled over a 

 Dutch metal leaf until it is fairly covered. 



The machine being now fully equipped, warm it 

 thorouglily before a clear fire in a room free from 

 draught, as a moist atmosphere is fatal to experiments 

 with an electric machine. Then procure a piece of wire, 

 eighteen to twenty-four inches long, thickly coated with 

 gutta-percha. Failing this, attach one end of a piece of 

 bare wire to the rubber-cylinder, and warm over the wire, 

 at about six inches from the other end, an ordinary stick 

 of sealing-wax, to serve as an insulating handle. Bend 

 the free end into a ring, or fasten it to a conducting ball, 

 such as a brass ball or even a rounded piece of apple or 

 potato. Bring this, while the machine is being turned, 

 )\ear enough to the prime conductor to enable sparks to 

 pass, and copious and brilliant discharges can be observed. 



Similar, but possibly not always such satisfactory, results 

 can be obtained by connecting the rubber with a gas or 

 water-pipe, or some other conductor, reaching to the 

 earth, and then bringing an earth-connected rod near the 

 prime conductor. These two experiment.s, be it observed, 

 are identical in ])rinciple. A very interesting and some- 

 what striking experiment is illastrated in Fig. 2, where 

 a piece of glass tubing, half an inch in diameter and ten 

 or twelve inches long, has pasted round it in spiral form 

 a series of small diamond-shaped pieces of tinfoil, placed 

 about an eighth or quarter of an inch apart. Over one 

 end is fixed, bj' means of cement — say, plaster of Paris — a 

 brass cap (Fig. 3), consisting of a jiiece of brass tnbing 

 half to three-quarters of an inch long, soldered to 

 a circular piece of this sheet-metal, three-eighths to 

 half an inch larger in diameter than the brass tubing. 

 Then is fitted loosely over the outside of this brass 

 tubing another piece of glass tubing of the same 



length as the smaller tube. Finally, another cap, 

 similar to Fig 3, is fitted on the free end of the 

 apparatus. The object of the outer glass tube is two- 

 fold. In the first place, it protects the pieces of tinfoil ; 

 and, in the second place, it facilitates the operation of 

 rotating the inner tube with one hand while the outer 

 tube is clasped in the other hand. To work the apparatus, 

 hold one of the conducting knobs in the hand (or by some 

 other means make an earth connection), and place the 

 other knob near the prime conductor. On the machine 

 being turned, numberless sparks will dart across between 

 the pieces of foil, the attractiveness of the effect being 

 greatly enhanced by revolving the tube. 



The tube may be made to revolve automatically at the 

 cost of a little more care and labour. The aj^paratus is 

 illustrated in Fig. 4. For this a separated insulating stand 

 may be used, or a small hole may be bored in the top of 

 the prime conductor.* Into this fit a short piece — say, 

 three-quarters of an inch long — of iron (the diameter being 

 such as to fit the hole loosely). To the upper end of the 

 rod solder a round piece of thin sheet brass about an inch 



TT 



Fig. i. 



Fig. 



in diameter, and having soldered to its upper surface a 

 jiiece of brass tubing three-quarters of an inch long and 

 large enough to fit the outer glass tube of the spiral fairly 

 well (either inside or outside). The inner tube is pro- 

 vided at the bottom with a pivot, which may consist of a 

 short pointed piece of steel attached to a wooden plug 

 fitting inside the tube. A hole should be drilled through 

 the brass disc large enough to allow the pivot to rotate 

 freely, the point working on the smooth end of the sub- 

 jacent iron. The lowest piece of foil on the tube .should 

 bs connected electrically with the pivot. 



The upper end of the inner tube should be fitted with r. 

 cap, consisting of a piece of bra.ss tubing surmounted by 

 a round piece of thin sheet brass, the brass tubing 

 extending for an inch or so above the outer glass tube. 

 On to the cap solder a number (three or four) of thin 

 wires about eight inches long, and with about half r,n 

 inch at each end bent horizontally and at right angles, 

 all the bent portions, or " points," pointing in one 

 direction (as viewed in walking round a concentric 

 circle). The parts should all be as light as po.ssible, and 

 should balance well. If the apparatus thus made be put 



* It would be advantageous to let in, in this case, a piece of a 

 small brass tubing having an internal diameter of three-sixteenths 

 or a quarter of an incli. It would in some instances prevent damage 

 being done to the cylinder. 



