Hydro- Electrical Currents, 101 



slow disintegration of the bismuth, suggest to me the view, that the 

 thermo-electrical current in a joint, as a general principle, passes from the 

 side which is changing towards that which remains more stationary ; and to 

 develope it in its highest energy, the couple should consist of a change- 

 able half (bismuth) and of a fixed half (antimony). To this view it may 

 be objected, that the experiments given above shew that antimony is a 

 metal which can be forced through considerable changes in density, but 

 they also shew that such alterations are injurious to its action as a negative 

 thermo-electric (32) ; and further, it differs from other metals in gaining 

 density by annealing, so as to approach to its natural statical state. 

 When both sides of a thermo-couple are changing, then the current re- 

 presents the balance betwixt the two actions. Where a reversal of the 

 current is obtained by varying the temperature, the balance of change 

 is first on one side then on the other ; a good experiment of this kind 

 is shewn with an antimony and iron thermo-couple. The iron is the 

 thermo-negative metal for all temperatures below 160° ; at this point the 

 two sides of the joint change alike ; and for higher temperatures anti- 

 mony is the negative metal. An extension of this experiment, with iron 

 and antimony elements, shews its great value for explaining the nature of 

 thermo-electrical action; for when the antimony has been cast in a cold 

 mouldj the reversal of the current, at a temperature about 160°^ is then 

 constant and most decided ; but if the antimony is cast in a mould heated 

 nearly to redness and slowly cooled, the iron is on the positive side from 

 the commencement of the heating of the elements, the reversal of the 

 current disappears. 



The view I have attempted to trace above, as governing in all thermo- 

 electrical arrangements, appears to me to be applicable to hydro and 

 frictional sources of this agent, where the current passes from the side 

 disintegrating or changing towards the stationary element of the arrange- 

 ment which continues unaltered ; and that the numerous instances of 

 variations in the direction of frictional-electrical currents may be ex- 

 plained on the same principle as the reversal of a thermo-current by a 

 change of temperatui*e, viz., that the greatest amount of change is in the 

 rubber when it excites glass, and, again, when the same rubber excites 

 resin, that the resin then undergoes the most rapid change. 



From the last experiment with iron and antimony, it will be apparent, 

 that in batteries, fig. 1, to be excited by the weather, the iron might with 

 advantage supply the place of the antimony ; and I would recommend it 

 to be so applied, but for the practical difficulty of soldering pure bismuth 

 to iron. From some other experiments with bismuth, as the thermo- 

 positive metal, attached to lead, tin, and alloys of these metals, I could 

 recognise no diminution in the thermo-electrical energy for these couples, 

 when heated in oil to 95°, compared with a couple of bismuth and anti- 

 mony; so that if the form of the battery, fig. 1, described at the com- 

 mencement, should prove troublesome, on account of the fragile nature 

 of the long bars, lead may well supply the place of the antimony used 

 for them. Copper and zinc, in connection with bismuth, stand a little 

 below lead. Antimony cast in a hot mould is much more brittle than 

 when cast in the same mould cold. R. Adie. 



