MS 



UNDULATORY FORCES. ELECT1UCITY. 



[TIIEKMO-KUECTI: : 



formed by tlicir union; anil bonco tlio choice of the 

 metals, bismuth and antimony, for construct ing batteries. 



TABLE OF TIIERXO-KLECTIUO JUSTALS. 



Bismuth. 

 1. >1. 

 Tin. 



;>or. 

 Zinc. 

 Iron. 

 Antimony. 



Tliis singular method of producing electric currents 

 ban boon of great value in many respects. In the section 

 on Heat, wo have already pointed out how it may be 

 employed in measuring changes of temperature, far too 

 niinuto to be appreciated by ordinary tlicrmoinetric 

 arrangements, lint, bogidcs these philosophical applica- 

 tions, thermo-electric batteries have been arranged with 

 other apparatus, for a variety of practical purposes in 

 daily life, one or more of which wo shall have to allude 

 r our remarks on the Electric Telegraph. 



The best method of showing the existence of athcrmo- 

 currcut, u to attach tho wires of the battery to a gal- 



vanometer. As soon a* heat is applied, iu tho wny wo 

 have descrilx-d, thu iicodle is instantly diverged, just as 

 if an ehictrio current from a voltaic battery wore pass- 

 ing. The method of applying a thermo-electric cm 

 for many experiment*, iu connection with radiant ! 

 is illustrated iu tho following cut ; to tho luft of which 

 Flf.W. 



wo seo the source of heat, which, passing through screens 

 of substances under experiment, arrives at tho battery. 

 Tho current thus produced act* on the galvanometer, 

 seen on the right hand of the engraving. 



ADDENDA ON ELECTRICAL MACHINES. 



WB have already mentioned, at page 171, a plate elec- 

 trical machine, which was, at one time, in tho Royal 

 Panopticon, London ; and Sir. Warner, under whoso 

 superiutendencd it was constructed and worked, has 

 favoured us with some interesting particulars respect- 

 ing it 



Tho plate itself was ton foct in diameter, and the 

 machine was provided with double rubbers and con- 

 ductors. For tho purpose of keeping tho glass surface 

 free from moisture, steam was allowed to pass into tho 

 rubbers, which were constructed of sheet iron. The 

 entire machine was supported by plate-glass columns, BO 

 as to insure complete insulation ; and the plato was 

 driven by steam power. The number of revolutions 

 averaged about forty per minute, for ordinary experi- 

 ments ; and the rubbing force, or friction, was regulated 

 in the usual manner by screws, <tc. 



\\ itli respect to tho force developed, wo may observe 

 that this machine iiev.-r had a fair trial. It was, un- 

 avoidably, placed in tha centre of an immense hall, 

 round wliicu currents of moist air were continually 



passing ; and in front of tho machine was a basin, from 

 which many hundred gallons of water were forced per 

 minute, twice each day, during the exhibition of the 

 Chromatic Fountain. With all these disadvantages, tho 

 effects were surprising. Above two hundred feet of 

 Leyden jar surface could bo charged in a few seconds ; 

 twenty feet of steel wire could be rapidly deflagrated by 

 tho battery discharge j and other electrical phenomena 

 were produced on an equally largo scale. Under tho 

 best circumstances, in dry weather, a spark of upwards 

 of two feet in length, and of great density, con I 

 obtained from tho prime conductor ; and the usual class 

 experiments with the direct spark, allbrdcd brilliant 

 results. On the broaking-up of the institution, this 

 machine passed into the hands of its constructor ; but it 

 is to be hoped that, eventually, its powers will be 

 more fully tested than they have yet l>een. Such would, 

 no doubt, result iu our acquiring additional facts in 

 reference to the powers and cU'ects of electricity pi'o 

 duced by friction, and possibly lead to discoveries of 

 groat interest. 



