ELECTRICITY. 



511 



Practical poses, is represented in Fig. 3, where AB is the glass 

 Electricity, cylinder, about 12 inches long and 7 inches in diameter, 

 ^~"'~ v '~ ' supported by the glass pillars E, F, and moved by the 

 CCXLVII. simp' 6 winch W. This machine is provided with two 

 Fig. 3. conductors, one of which D is the positive conductor, 

 and the other C, the negative conductor, attached to the 

 back of the rubber, which is not visible in the Figure. 

 Both these conductors are hollow, and admit their ends 

 to be taken off, so as to introduce a coated Leyden phial, 

 which we have represented in the Figure at P as lying 

 within the positive conductor D. Each of the conductors 

 has a brass knob k, and is supported upon glass pillars 

 R, S. These pillars are fixed at right angles to sliding 

 pieces of wood, which move in grooves formed in the 

 stand GH, and are kept tight in any position by the 

 screw nuts N, N. One of these screw nuts keeps the 

 ruli!>er in contact with tne cylinder, while the other gives 

 stability to the positive conductor. The flap o n is seen 

 extending over the cy under from the negative conduc- 

 tor. 



4. Description of Dr Priestley's Electrifying Machine. 



Dr Priest- As the electrical machine invented and used by Dr 

 ley's c-kctri- Priestley, was for a long time in great repute, and as it 

 ">z '""- affords an example of a machine with a glass globe, we 

 have given a drawing of it in Fig. 4. The glass globe 

 *'3- * AIJ is fi\cd upon the extremity of an axis at A, which 

 s through the upper part of the vertical stand EF, 

 and carries a small wheel IP. The rubber m consists of 

 a hollow piece of copper covered with basil skin, and 

 filled with horse hair. It is supported by a socket, 

 which receive;, the cylindrical axis of a circular plate of 

 glass f, the other end of which is fixed into a spring R, 

 which is made to press the rubber against the globe 

 by tightening the screw .v The prime conductor C is a 

 pear-shaped hollow vessel made of polished copper, and 

 supporU-d by a pillar insert d in a firm stand of baked 

 wood. It is perforated with several holes for receiving 

 hooks and wires. It receives its electricity from the 

 globe, by means of a long arched wire CD, terminating 

 in an open ring on which several sharp pointed wires 

 are hun^r, so as to play lightly upon the globe when it 

 is revolving. The globe is put in motion by a multiply- 

 ing wheel W, turned by the handle seen above W, which, 

 by the intervention of the string W w, drives the small 

 wheel w, and thus gives any degree of velocity to the globe. 

 "Wlien Dr Priestley wished to have positive electricity, 

 he connected the rubber with the table or floor by 

 means of the chain m n, and when he wanted negative 

 electricity, he connected the rubber by a chain with 

 an insulated conductor, and the conductor C' with the 

 table or ground. In tiie machine, as originally con- 

 structed by Dr Priestley, he made provision for recei- 

 ving globes of different diameters, and also for using 

 several at the game time, as well as for employing those 

 of such a large size that they required support at both 

 ends of their axis. Mr Lane's electrometer, in its earliest 

 state, is represented as annexed to the machine at L. 

 See Priestley's History of Electricity, p. 531. 



5. Description of Read's Electrifying Machine. 



Rnd' dec- This machine, though assuming a very different ap- 

 ifyingma- pearance from any of tho.-e which we have descri- 

 bed, does not exhibit any essential improvements. It 

 i.s, however, a convenient and compact machine, and 



ccxVvn has been vcr - v g enen % used - The cylinder AB is 



tig. S. ' P lf ? ce<1 vertically, and has the upper extremity of its 



axis moveable in die end of the bent iron support 



EF. The rubber m is attached to an iron spring Practu-;J 

 R, and is pressed against the cylinder by a screw S, jSlectricit^ 

 but it has the disadvantage of not admitting of in- "*"Y"^ 

 sulation. The cylinder receives its motion from the 

 multiplying wheel W, and small wheel w, by means of 

 a string. The conductor CD has a very peculiar form. 

 It is opened and bent downwards at one end, so as to pre- 

 sent a series of points p, p for receiving the electricity from 

 the cylinder; and it is screwed into the head of a Leydeii 

 jar J, coated as usual. When it is not required to give 

 a shock, the coated jar J is removed, and an uncoated 

 jar put in its place, so as to serve merely for an insula- 

 ting support for the conductor. Lane's electrometer is 

 represented at L, as connected with the machine. Sec 

 Priestley's History of Electricity, p. 529. 



6. Description of Beccaria's Electrifying Machine. 



This machine, of which it is completely unnecessary to Beccaria's 

 give a drawing, is interesting principally from its having electrifying 

 been employed in the experiments of Beccaria. It con- UMcJune ' 

 sists of a cylinder turning horizontally between two up- 

 right supports, by means of a large multiplying wheel. 

 This machine was supported upon a clumsy rectangular 

 frame of wood, which rested upon four glass feet. Each 

 of these glass feet was placed in semicircular boxes of 

 tin, put together so as to form a circular box ; and when 

 the machine was in use, these tin boxes were filled with 

 warm ashes, in order to produce a more perfect insula- 

 tion, by keeping off all moisture from the glass. The 

 prime conductor, which was suspended by silk strings, 

 consisted of a cylinder of tin 12 feet long, and afoot in 

 diameter, and had a conical end towards the cylinder 

 of glass, the opposite end having a hemispherical form. 

 The whole machine being insulated; positive electricity 

 was obtained, by making a communication with the 

 ground by means of a chain ; and when negative elec- 

 tricity was wanted, the whole machine became a nega- 

 tive conductor, by making the positive conductor com- 

 municate with the ground. 



7. Description of the Rev. Mr Pearson's Machine. 



This machine is chiefly intended for medical purpo- **r Pear- 

 ses, and for administering electricity in cases of sus- s 9' smil * 

 pi-nded animation. It consists cf a cylinder 7^ inches ne " 

 long, and four inches in diameter, turned by a simple 

 winch. Instead of a conductor of the common kind, it 

 has a small insulated collector, which is a piece of 

 smooth wood, covered with tinfoil, and rounded at the 

 ends. It is about six inches long, and one inch in dia- 

 meter, and collects the electricity from the cylinder by 

 means of about twelve fixed pins of brass. It is then 

 connected by a chain with a plate of glass 9^ inches by 

 7^, cemented to the wood at the four corners of the 

 box, by electrical cement, and coated on both sides with 

 tin-foil, as in Plate CCXLIII. Fig. 7. This plate serves 

 for aLeyden phial. See Nicholson's Journal, vol. i.p. 506. 



Various other machines, formed with globes and cy- 

 linders, have been employed by different experimental 

 philosophers ; but as they differ from those which we 

 have described only in the awkwardness of their con- 

 struction, it would be an insult to our readers to offer 

 any particular drawing or description of them. 



The original electrical machine used by Otto Cue- otto Guc- 

 ricke, was merely a globe of sulphur, of the size of an rickc's ma- 

 infant's head, formed by melting sulphur in a glass globe, chine, 

 and afterwards breaking the glass. It was then placed 

 upon an iron axis, after being perforated in two places. 



