354 Mr R. Adie on Thermo- Electrical Experiments, 



briefly recapitulated. A piece of soft steel with a portion hardened 

 and reduced in density, by heating and plunging in water, gives a 

 thermo current passing from the hard or changing side to the soft 

 or more stationary side. A similar experiment with the part hard- 

 ened and made dense by hammering, gives the current passing from 

 the soft part to the hard. Bars of hard steel change their dimensions 

 by annealing at temperatures 20° above the weather. This I have 

 carefully observed by reading off their length with delicate microme- 

 ter microscopes. Further, I am informed, on excellent authority, 

 that the steel balance-springs of chronometers are subject to a change 

 extending over years ; it is by the rates at different temperatures 

 that this slow change is found out, — a truly beautiful method of de- 

 tecting minute alterations. 



Antimony, when cast in a cold metal mould, has a low specific 

 gravity which rises by annealing ; when cast in the same mould 

 heated, the specific gravity is high, and reduces slightly by anneal- 

 ing at high temperatures. When an annealed bar of antimony was 

 connected with a soft bar of iron and the joint heated, the iron was 

 the generating metal ; but when a quickly cooled bar of antimony 

 was substituted for the annealed piece, then the antimony became the 

 generating metal, being a reversal of the natural relation, and con- 

 tinued so until the temperature reached 160°, where, although there 

 was unequal heating, and molecular change in so far as regards the 

 density of the bars, there was still no electrical current, most pro- 

 bably from the change in the two elements exactly counterbalancing ; 

 for higher temperatures the usual relation of iron to antimony was 

 established. These experiments with iron and antimony have always 

 appeared to me to be valuable for reconciling the action of a pair of 

 thermo-electric elements with an ordinary galvanic couple ; where 

 the molecular action corresponds to the chemical action, and the un- 

 equal heating in the thermo couple has to perform the same office 

 which the fluid has in those batteries excited by active chemical 

 agents, namely, to produce the electricity in a form that will circu- 

 late in a current. The facts shewn by the couples, where mercury 

 forms one of the elements, present difficulties which may serve to 

 stimulate more able inquirers to endeavour to explain. 



The results which I formerly gave of metallic silver, precipitated 

 by astral and solar influence, acting on the thermo-electric batteries 

 described No. 70, fig. 1, I have since repeatedly verified ; but for 

 this climate the quantities of metal obtained are much too small to 

 serve any purpose, beyond proving that silver may be so precipitated. 

 The experience of three years now makes me prefer the arrangement 

 described (No. 70, p. 348), as a sensitive instrument for telling at 

 all times the rate of radiation to or from the earth. 



There are molecular changes in metals, either immersed in water 

 or exposed to the moisture of the weather, which are very rapid. A 

 piece of thin brass wire exposed to the weather soon becomes brittle, 



