ELECTRICITY. 



ELECTRICITY. III. 



CTLINDEB ILECTBICAL MACHINE PLATK MACHINE ABM- 

 BTRONO'B HTDBO-ELECTBIC MACHINE. 



IT U now time for ua to para on to consider the mode in which 

 we can obtain elootrioity in largo quantities. This U done by 

 means of an electrical machine, which consists essentially of three 

 part* : firstly, the substance to be rubbed, usually a cylinder or 

 sheet of Kin.** ; secondly, the rubber ; and, lastly, the con- 

 ductor or reservoir to hold the elootrioity. 



Originally a globe of sulphur was employed as the substance 

 to be rubbed, but it was soon discovered that a globe of glass 

 would answer better, and this 

 was accordingly substituted. 

 At present, however, a cylin- 

 der ia usually employed (Fig. 

 6). These are made specially 

 for tin' purpose, and can be 

 obtained for a moderate 

 amount at glass -works, or 

 at philosophical instrument 

 makers'. In shape they resem- 

 ble a square-shouldered bottle 

 with a neck at each end. Caps 

 ore turned out of some hard 



the conductor to the knuckle or any other body bald to its or 

 if bent wires with balls at the end be inserted in the two oon. 

 duotors, a* shown at o and *, a series of sparks will pass between 

 them. It is necessary, if positive electricity is to be need, that 

 the rubber should be connected with the ground, and this is 

 usually done by means of a chain or a piece of wire. In the 

 same way, if negative electricity U required, the conductor mart 

 be uninsulated. 



As we hope that a great many of our readers will set to work 

 and make one of these machines for themselves, we will give 

 rather fuller instructions as to the mode of proceeding. Be' 

 assured of one thing at starting, and that is that you can easily 



succeed if yon only persevere, 

 and are not d ithpartgned by 

 apparent failure at first. 



We should recommend yon 

 to procure a proper cylinder 

 if possible; one nine or ten 

 inches long by six or seven 

 inches in diameter is a very 

 good size, and should not cost 

 more than about five shillings ; 

 considerable power may even 

 be obtained from a 

 one. Failing this, a Urge round 





wood to receive these, and should be so shaped that their ends 

 may serve as bearings for the cylinder. The winch is fixed to 

 the squared end of one of the caps. 



At one side of the cylinder is placed the rubber, c, which 

 consists of a cushion of wash-leather stuffed with horse-hair or 

 tow, and a piece of black silk (not represented in the figure) 

 psssen from the under side of this over the cylinder nearly to 

 the points on the other side. A conductor, A, is sometimes fixed 

 behind the rubber, and serves to collect the negative electricity. 

 On the other side of the cylinder is the prime conductor, B, 

 with a row of points along one side to receive the electricity. 

 Holes are bored at different parts of this, in order that brass 

 balls and rods or other pieces of apparatus may bo inserted 

 when required. 



On turning the cylinder, if the machine has been carefully 

 warmed and dried, and a little amalgam spread upon the 

 rubber, vivid sparks, several inches in length, will pass from 

 QO u g 



bottle will answer, but not so well, nor is it nearly so con* 

 venient. Some people recommend, when a bottle is used, that 

 a hole should be punched through the bottom, but there is con- 

 siderable difficulty and risk in doing this. The better plan is to 

 procure a disc of wood a little larger than the bottom of the 

 bottle, and fix it on by means of electrical cement. This 

 I cement is used for many purposes, and may be easily made. 

 It consists of resin, plaster of Paris, bees'-wax, oil, and red 

 lead. The resin is first melted in an earthen pipkin, a small 

 lump of bees'-wax and a little oil being added to render it more 

 tough. When fully melted, the plaster is stirred well in, 

 together with some red lead, to impart a better colour to it 

 The bottle and disc of wood should then be well warmed, and the 

 cement poured upon the former, and if the disc be kept from 

 slipping until it gets cold, the cement will hold firmly. The 

 larger the proportion of plaster used the harder will be the 

 cement. The winch is put on an axle affixed to this disc, and 



