NATURAL PHILOSOPHY. 121 



All the metals were the same as those used for my thermo-electric experi- 

 ments, with the exception of cadmium, which was purified. The alloys of 

 bismuth-antimony, bismuth-tin, antimony and zinc, were determined in or- 

 der to ascertain whether, as they give with other metals such strong thermo- 

 electric currents, they might be more advantageously employed for thermo- 

 electric batteries than those constructed of bismuth and antimony. Coppers 

 Nos. 1, 2, 3, were wires of commerce. No. 1 contained small quantities of 

 lead, tin, zinc, and nickel. The low conducting power of No. 1 is owing, as 

 Prof. Bunscn thinks, to a small quantity of suboxide being dissolved up in it. 

 Graphite No. 1 is the so-called pure Ceylon ; No. 3 purified German, and No. 

 2 a mixture of both. The specimens were purified by Brodie's patent, and 

 pressed by Mr. Cartmell, to whom I am indebted for the above. The con- 

 ducting power for gas-coke, graphite, and Bunsen's battery-coke increases 

 by heat from to 140 C. ; it increases for each degree 0-00243, i. e., at C. 

 the conducting power == 100, and between the common temperature and a 

 light-red heat about twelve per cent. The following metals were chemically 

 pure : Silver, gold, zinc, cadmium, tin, lead, antimony, quicksilver, bismuth, 

 tellurium. Those pressed were sodium, zinc, magnesium, calcium, cadmium, 

 potassium, tin, lead, strontium, antimony, bismuth, tellurium, and the alloys 

 of bismuth-antimony and bismuth-tin. The way in which these wires were 

 made is described in the Philosophic Magazine for February 1857. P/u7. 

 Mag. Vol. XVI., p. 219. 



ON THE ELECTRICAL DISCHARGE, AND ITS STRATIFIED APPEAE- 



AXCE IN RAREFIED MEDIA. 



The following is a report of an important paper recently read before the 

 Royal Institution, by Mr. W. R. Grove, F. R. S. : The best mode of exam- 

 ining and attempting to explain the electrical discharge, is to compare it 

 with its nearest analogue flame, to which one form of the discharge, viz., 

 the voltaic arc, has much seeming resemblance. The flame of a common 

 candle results, as is well known, from the chemical combination of carbon 

 and hydrogen with the oxygen of the air; and the combustion is most bril- 

 liant where the heated gases and particles are in proximity to the oxygen. 

 It forms a hollow cone, as the oxygen of the air, being consumed or com- 

 bined into water and carbonic acid at the exterior portion, cannot reach the 

 interior; the course of the currents of heated air, and the particular form of 

 this hollow cone of flame, are beautifully shown by the refraction it pro- 

 duces on a more brilliant light, such as that of the electric lamp ; the flame 

 issues from a single nucleus, the wick; and the amount of heat produced is 

 definite for a definite amount of chemical combination. 



In the voltaic arc there are two points or foci; the polar terminals there 

 undergo a change, but not a consumption equivalent, or nearly so, to the heat 

 and light produced; but if the consumption of the zinc, or the quantity of 

 it combined with oxygen in the cells of the battery, be compared with the 

 amount of heat generated in the arc, plus that in the cells of the batteiy and 

 conducting wires, the same amount of total heat will be found to be devel- 

 oped as if the same quantity of zinc were simply burned in oxygen. 



By subdividing more and more the plates of the voltaic battery, and pro- 

 portionally increasing their number, we gradually increase the length and 

 diminish the volume of the arc, until at length AVC arrive, as in the voltaic 

 columns of De Luc and Zamboni, at the electric spark. 



11 



