Mr R. Adie on Electrical Experiments. 299 



with a small quantity of water, sufficient to cover their bulbs. Both 

 thermometers soon indicated an elevation of temperature, the one in 

 the positive capsule standing the highest; after 15' action, the ob- 

 served temperatures were, — apartment, 42° ; negative pole, 69° ; 

 positive pole, 62° ; in this case, the capsules were 2^ inches, as 

 under ; on approaching them together, till nearly in contact, the ra- 

 pidity of the decomposition increased ; and after a similar interval 

 of 15', the negative pole was 62° ; the positive, QQ°. The temper- 

 atures stated were verified by counter-experiments, with the poles 

 reversed, to guard against any error which might arise from inequal- 

 ity in the capsules, or in the extent of their surfaces in action. 



The next experiment was made with the same battery, and it 

 was designed to ascertain if the double volunm of hydrogen evolved 

 at the negative pole, could occasion the reduction in temperature 

 there noticed. The platina capsules were replaced by two larger 

 copper ones, superficies in action 3J inches ; these were made to de- 

 compose in a saturated sulphate of copper solution, where there is no 

 gas given off; the thermometers were arranged as for the first re- 

 sults. The temperatures observed, after an interval of 15', were, 

 for the room, and a large vessel containing a solution of sulphate of 

 copper, 46° ; negative pole, 46° ; positive pole, 47° ; the small bulb 

 of a thermometer placed betwixt the two capsules 48°; counter-ex- 

 periments, like those for the first set, were made, to verify these 

 small differences of temperature. The extent of the changes could 

 not be expected to approach those given for the platina capsules, 

 where the surface in action was 3 J times less, with the resistance to 

 conduction greater. 



36. A piece of platina wire, 1 J inches long, was connected by two 

 stout copper wires, with the poles of a five pair galvanic battery, 

 which I found sufficient to keep the temperature of the platina at a 

 full red heat ; in this common experiment there is always a portion 

 of the thin wire, where it joins the stout copper wire, which remains 

 dark, the present operation was arranged, to ascertain if the dark 

 portions on both sides were equal ; to prevent the interference of cur- 

 rents of air, a glass shade was used to cover the whole. 



P, fig. 1, is the stout wire from the positive pig. i_ 



pole ; N, the negative wire ; A, the dark por- 

 tion of the platina wire on the positive side, 

 which always appeared shorter than the dark 

 portion C, on the negative side ; B, the incan- 

 descent part of the wire. I reversed the poles 

 and repeated this experiment several times, al- 

 ways with the same result. To me it appears to P 

 be the readiest proof of the difference of tem- 

 perature betwixt the extremities of an electri- 

 fied wire ; but, as it is impossible to give measurements of the re- 

 lative lengths of the dark parts A and C, I removed the thin wire 



N 



