Viewing page 17 of 195
This transcription has been completed. Contact us with corrections.
28 April 28th 1843 April 29 Repeated some of the other experiments of Mallone and gained some experience in the use of the apparatus. Tried with the Mellony galvanometer the thermopile which I purchased in London, found this nearly as sensitive as the new one from Paris - Also tried the single pair of plates, which I constructed some year or two ago - found that the approximation of the hand to this produced a wide deflection of the needle. [[image - cylinder with positive and negative charges]] Placed a small cup of platina on the face of the London pile [[page torn]], poured into this a few drops of water, the evaporization of the liquid produced a permanent deflection of 30 [[degree symbol]]. The pile was supported by passing it perpendicularly through a disk of pasteboard, which rested on the rim of a glass tumbler. When a crystal of muriate of soda of the size of grain of rice was thrown into the water in the little cup, a deflection of 20° degrees was produced by the reduction of temperature due to the solution of the salt. It is on this principle that M Peltier of Paris has formed an hygrometer which gives the rapidity of evaporation by the deflection of a needle connected with a cup, containing water and placed on the thermopile. Some experiments were also made, relative to the solution of tin foil in mercury. this gave cold although the mere contact of mercury with lead appeared to produce a slight increase of temperature. of this result at present I am not confident, further experiments will be required in order to establish it. [[end page]] [[start page]] May 1st 1843} Heat from the magnetization of Iron-- 29 Attempted to get an indication of an increase of temperature in the act of magnetizing a small bar of soft iron. for this purpose, two long wires were attached to the galvanometer, in order that the polarity of iron might not affect the position of the needle. [[margin]][[image--magnet suspended]][[/margin]] The magnet was suspended from a lamp stand, with the thermo-pile placed under it, and across this was laid the small bar of soft iron; the whole apparatus was supposed to obtain the temperature of the room, and then the thermo-pile with the cross bar of soft iron, was raised up by moving up the ring of the brass ring stand until the iron touched the magnet, care being taken not to impart sensibly any heat to the several parts of the arrangement. When the experiment was made the needle was observed to move slowly from rest at zero to [[edited from 25 to 15?]]°. This effect was produced 3 times in succession; the motion of the needle was not as if by a single impulse as in the ordinary cases of the action of the pile when affected by radiant heat, but as if from a source of heat gradually conducted through or from the interior of the iron. *If there be no falacy in this experiment, it shows the evolution of heat by the change produced in a bar by the process of magnetization. There are however several sources from which the heat may be derived as well as from the magnetization of the iron. 1st. It may come from the percussion of the iron and the magnet. 2nd. from the condensation of the air which takes place when the bar is suddenly brought in contact with the face of the horse shoe. I must make farther experimts on these points tomorrow. The experimt may be made with the horse shoe in a vacuum, and by bring the iron fully in contact with the face of the horse shoe, the sources of heat before mentioned will be obviated. * Repeated these experiments on 2nd of May (page 32), found no Result of the kind.
