I have already had the honour of presenting to the Royal Society an account of researches carried on with a view of determining the effects of stress and strain on the elasticity and electrical resistance of metals. Side by side with these researches were conducted others on magnetic induction and thermo-electricity, and a very considerable amount of experimental detail was collected with reference to the two last physical properties of matter. The results of the last mentioned investigations have, however, now remained unpublished for several years, for it seemed desirable that, previously to publication, certain phenomena should, if this were possible, have light thrown upon them by further experiments on elasticity. More especially was I anxious to examine into the causes of the loss of energy experienced by a wire when vibrating torsionally, for the interesting memoirs of G. Wiedemann † and D. E. Hughes led me to expect that my doing so would cause some insight to be gained regarding the above-mentioned phenomena. The results of these labours, which have now occupied almost the whole of my spare time for the last three years, I offer to the Society in the hope that they may prove as interesting to others as they are to myself. Researches of . Thomson and Wiedemann. Under the title of “The Elasticity and Viscosity of Metals,” Sir W. Thomson published a memoir, the first portion of which deals with the loss of energy of a wire when vibrating under the influence of torsional elasticity. It is pointed out ( a ) that, though no change of volume or shape can be produced without dissipation of energy, because of the accompanying change of temperature, estimates founded on the thermodynamic theory of elastic solids suffice to prove that the loss of energy due to this cause is small in comparison with the whole loss of energy which has been observed in many cases of vibration, ( b ) That, as a result of experiments in which a spring was vibrated alternately in air of ordinary pressure and in the exhausted receiver of an air-pump, there is an internal resistance to its motions immensely greater than the resistance of the air. Hence it is concluded that with solids as with liquids there exists an internal resistance to change of shape depending upon the rapidity of the change . The results of Thomson’s experiments are briefly as follows:—