406 



ELECTRICITY. 



ninth time the wire was misured, ami was fount! to bo 

 iborteoed in the proportion of Ath of an 'ulis- 



charge. Thr itnnir liiitli i j n mi lln n illnll*lgi I i times 

 more through the same w ire. which continued to shor- 

 ten nearly in tlie same proportion, the total dimtnu- 

 tion of length being fully 1 inch and ,'.th. Hi 1 could 

 not Hud, by n jwir of scales that turned with less than 

 Jth of a grain, that there was any difference in its 

 weight. It .tppearrd, however, to have increased in 

 thickness, and it is probable, that its contraction in 

 length was owing to successive expansions. Mr Nairne 

 also found, that a piece of copper wire plated with 

 silver, and of the same dimensions as tlvf iron wire, 

 was shortened only ,',th of tin inch by one charge of 

 26' feet of coated glass, which is only *d* of the effect 

 produced upon the iron wire. 



Mr Brooke found, that a battery of nine bottles, ex- 

 posing 1C square feet of coated surface, when dischar- 

 ged nine times through a piece of steel wire 12 inches 

 long, and , i . th of an inch thick, diminished its length 

 one inch and a half. 



Erj>. 10. If any other substance, inferior in conduct- 

 ing power to the metals, such a- water, be placed in 

 glass tube, and if a shock is sent through the wires as 

 formerly, the tube will be broken in pieces by the ex- 

 pansion of the water. The same result will be obtain- 

 ed if a common drinking glass, filled with water, is used 

 d of the tube. 



Beccaria made this experiment with a drop of water 

 in the centre of a solid glass ball, and the ball was bro- 

 ken in pieces. In the same way Mr Morgan has suc- 

 ceeded in breaking green glass bottles filled with water, 

 when the distance of the wires, between which the 

 shock passed, exceeded two inches; and Mr Singer 

 has burst glass tubes half an inch thick in the sides 

 with a bar of the same size : Beccaria varied the expe- 

 riment in a very pretty manner, by constructing a sn.all 

 mortar with a ball, and placing behind the ball a drop 

 of water, so as to be between the two wires which pas- 

 sed through the side of the mortar. The charge being 

 sent through the two wires, the drop of water was 

 expanded with such force, as to drive out the ball with 

 great velocity. By a drop of oil, M. Lullin of Geneva 

 projected the ball with still greater velocity. 



Exp. 1 1 . Into the mouth of a mortar of ivory with a 

 cavity an inch deep, and half an inch wide, fit a cork cap, 

 so as to shut up the aperture v ithout much friction, 

 and having made the wires pass through the sides of 

 the mortar, a shock sent through the wires will sud- 

 denly expand the air, and drive out the cork with con- 

 siderable violence 



Ftp. 12. Fill a capillary tube with mercury, and 

 make the charge pass through it by means of wires, .-is 

 formerly, and the expansion of the mercury will be suf- 

 ficient to burst the tube. 



Exp. 13. If the charge of a jar is made to pass over 

 the surface of a piece of soft dough, the tract of the 

 fluid will be marked with a permanent depression. 



Eif. 14. If a clean brass chain, dipped in melted 

 rosin, is laid upon paper, and if the charge of a battery 

 uf.T< square feet is sent through it, the resinous coat ng 

 will be driven off from every part of the chain which 

 will be left as clean as if no rosin had been upon it. 



Erji. 15. If the brass chain is laid upon a p.ece of 

 glass, and a similar charge passed through it, the glass 

 will be marked in a beautiful manner on every P"rt of 

 its surface where it had been touched by the chain, 

 every spot having the width and colour of t.'.t link. 

 The metal could be scraped off the glass t the outside 



of the marks, but in the middle part it was forced with- 

 in the pores of the ti' 



l)r I'ricstlcy. to whom we are indebted for the two 

 preceding experiments, gave the same tinge to glass 

 with . i silver chain, nnd small pieces of other metals, 

 but he could not -nivecd with lar^. 



I-'.T/>. Hi. 1'lace a piece of dn writing paper upon the 

 table of Henley's discharger, and having taken off the 

 balls, place the ends of the wires ag.iinst the pap- 

 that the distance between the wires may be two inches. 

 If a powerful shock is now sent from one wire to the 

 other, the paper will be torn in pic, 



AV;>. I". In a piece of wood, half an inch long, and 

 a quarter of an inch thick, drill two holes at its oppo- 

 site ends, and insert the ends of two wires in the hoi. -, 

 so that the points of the wires are at the distance 

 quarter of an inch. If a strong charge is now | 

 through the wire, the wood will be split in pieces. 

 Stones, sugar, and other non-conducting and brittle sub- 

 stances, may be broken in a similar manner. 



Eip. 18. Having placed a piece of plate glass, about 

 an inch square, and half un inch broad, upon the table 

 of 1 lenley's discharger, and having pressed it down with 

 a weight, set the points of the wires opposite to each 

 other, and against the under surface of the glass. If 

 the charge of a large jar is now sent through the \ 

 the glass will be broken into innumerable fragments, 

 and some of it reduced even to an impalpable powder. 

 When the glass is very thick, so as to rc-sist the effects 

 of the shock, it will be found marked with vivid pris- 

 matic colours, which, Mr Henley imagines, are produ- 

 ced by thin lamina- of the glass separated from it by the 

 shock ; but it is more probable that it is an oxidation. 



EJC. 19. If a very large charged jar has its outside 

 coating connected with the outside coating of another 

 jar about ten times less, and if a communication is made 

 by the discharging rod with their inside coatings, the 

 small jar will be broken, from the great quantity of elec- 

 tricity which is suddenly transferred to it. 



The curious experiments of 1'rofcvsur I .ichten!>erg of 

 Gottingen, on the arrangement of powders upon an 

 electrified plate, may be given without much impropri- 

 ety under the present Section. 



Let a plate of any resinous substince, as rosin, gum 

 lac &c. be excited either by friction or otherwise, and 

 let any metallic body of any shape whatever, a brass 

 ring for example, be placed upon the plate. Let this 

 ring l>e then electrified with an electricity opjxMite to 

 that of the plate, and afterwards removed from the plate 

 by a stick of sealing-wax, or any other non-conducting 

 body Let some powder of rosin, kept in a linen bag, 

 be now shaken upon the resinous plate, then if the plate 

 is excited negatively, and the brass ring positively, the 

 powder will fall only on those points of' the plate that 

 were touched by the brass ring, and will form beauti- 

 fully radiating appearances like stars, while almost no 

 powder will IK.- found on any other part of the plate. 

 If, on the other hand, the plate is electrified positively, 

 while the ring is electrified negatively, then the pow- 

 dered rosin will fall only on the parts of the plate which 

 were formerly uncovered, the figures of .stars being now 

 indicated by the absence of the powder 



These experiments, which were first known in Eng- 

 land in 1771, were immediately repeated and varied by 

 the Rev. A. Bennet, anil M. Cavallo. Mr Bennct has 

 given the following account of his method of rendering 

 these figures permanent. " To make red figures, take 

 a pound of rasped Brazil wood, put it into .1 kettle with 

 as much water as will cover it, or rather more ; also put 

 1 



of 



eiectriritr in 

 tearing and 

 ren<tiiig bo- 



I.ichttn- 

 bcrp's me 

 thixl of pro- 

 ducing cu- 

 rious confi- 

 gurations bjr 

 elixtiurit}'. 



Bcnn< 

 peiimentoi 



