« PreviousContinue »
each case the thermo-electric quality of soft iron intermediate between them.
These various results show that the character of the effect in each case is decided by distorting stress or by distortion, and leave entirely open, and only to be answered by further experiments, the questions : what is the thermo-electric effect of pressure or traction, applied uniformly in all directions to a metal ? and what is the thermoelectric effect of a permanent condensation or dilatation remaining in the metal, when freed from the force by which that condensation or dilatation was produced ?
Experiments are also described, by which the author found that in soft iron, under magnetic force, and in that retaining magnetism, steil when removed from the magnetizing force, directions along the lines of magnetization deviate thermo-electrically towards antimony; and that directions perpendicularly across the lines of magnetization in soft iron, deviate towards bismuth, from the unmagnetized metal. He illustrates this conclusion by an experiment on a riband of iron, magnetized nearly at an angle of 45° to its length, and heated along one edge while the other is kept cool. When the two ends, kept at the same temperature, are put in communication with the electrodes of a galvanometer, a powerful current is indicated, in such a direction, that if pursued along a rectangular zigzag from edge to edge through the band, the course is always from across to along the lines of magnetization through the hot edge, and from along to across the lines of magnetization through the cold edge.
4. In this part of the communication, attempts made by the author to find the effects of various influences on electric conductivities of metals are described. One of these, with a very unsatisfactory method for testing resistances, led to the conclusion that longitudinal magnetization diminishes the conducting quality of iron wire. The general plan for testing resistances, which he subsequently adopted as the best he could find, and which has proved very satisfactory, is next explained ; and as an illustration, a single experiment on the relative effect of an equal longitudinal extension on the resistances of iron and copper wires is described. The conclusion established by this experiment is, that both by extension with the tractive force still in operation, and by permanent extension retained after a cessation of stress, the conductivity of the substance is more diminished
in iron than in copper ; or else that it is more increased in copper than in iron, or increased in copper while diminished in iron, if it is not in each metal diminished, as the author is led by a partial investigation of the absolute effect in each metal to believe.
5. The result previously arrived at regarding the effect of longitudinal magnetization on the conductivity of iron is confirmed ; and an experiment that would have been found impracticable by the less satisfactory method, proves the same conclusion for magnetized steel wire, with the magnetizing influence away. Two very different experiments show further, that the electric conductivity of magnetized iron is greater across than along the lines of magnetization. A last experiment, showing that iron gains in conducting power by magnetization across the lines of the electric current, leads to the conclusion that there is a direction inclined obliquely to the lines of magnetization, along which the conductivity of magnetized iron would remain unchanged on a cessation of the magnetizing force.
March 6, 1856.
Colonel SABINE, R.A., V.P. and Treasurer, in the Chair.
In accordance with the Statutes, the Secretary read the following list of Candidates for election into the Society
John Hutton Balfour, M.D. Dr. Humphreys.
David Macloughlin, M.D.
John Carrick Moore, Esq. Samuel Brown, Esq.
Robert William Mylne, Esq. George Bowdler Buckton, Esq. Henry Minchin Noad, Ph.D. Sir John Fox Burgoyne, Bart. Edmund Potter, Esq. William Coulson, Esq.
Rev. T. Romney Robinson, D.D. Thomas Russell Crampton, Esq. Henry Hyde Salter, M.D. Richard Cull, Esq.
William Scovell Savory, Esq. Hugh Welch Diamond, M.D. Archibald Smith, Esq. James Dixon, Esq.
Robert Angus Smith, Esq. Sir Charles Fox.
Thomas A. B. Spratt, Capt. R.N. Philip Henry Gosse, Esq. Henry Ward, Capt. R.E. Robert Harkness, Esq.
Thomas Williams, M.D. Cæsar Henry Hawkins, Esq. Forbes Benignus Winslow, M.D.
The following communications were read :
I. Supplement to the “Account of Pendulum Experiments
undertaken in the Harton Colliery;" being an Account of
Adverting to the circumstance that, in the Harton Experiment, there was a mean difference of 7° between the temperature above and below, and that a careful determination of the coefficient for temperature-correction was therefore necessary, the author describes the process by which the correction was now investigated by experiment on the same pendulums which were used in the Harton Experiment. Two rooms were selected at the Royal Observatory, Greenwich, having firm stone floors, and admitting of being heated, one by a stove in the room, the other by a hot-air-apparatus below. One pendulum was mounted upon its iron stand, with clock and other apparatus, in one room, and the other in the other room. taken that the pendulums and their thermometers should be effectually protected from radiation. The two clocks were compared by carrying a chronometer from one to the other, and remarking the time of coincidence of beats; a method which admits of very great accuracy, when (as in this instance) the distance through which the chronometer is to be carried is small. In the Fifth Series (counting the series in sequence to those of the Harton Experiment), Pendulum 1821 was kept in heat, and Pendulum 8 cool, and continuous observations were kept up during forty hours. In the Sixth Series, Pendulum 8 only was kept in heat, and observations were again kept up during forty hours. The Seventh and Eighth Series were similar, respectively, to the Fifth and Sixth. The temperatures are referred to two of the thermometers used in the Harton Experiment, and to two other thermometers supplying the place of two of the Harton thermometers which cannot be found. The observations were con