- By touching different points of the wire with different reagents, the excitability of these portions are rendered unequal. Hence a resultant electromotive variation may be obtained by Vibrating the wire as a whole. The current in the Wire is from the less to the more excitable.
- By this method, invisible traces of physico-chemical change in a wire may be detected.
- Chemical reagents not only change the excitability but the quickness of response. Two points having two different rates of excitation will thus, under proper conditions, give rise to diphasic effects.
- I take this opportunity to thank the Managers of the Royal Institution for the facilities offered me to carry on the investigation at the Davy-Faraday Laboratory.
"On the Effect of a Longitudinal Magnetic Field on the Internal Viscosity of Wires of Nickel and Iron, as shown by Change of the Rate of Subsidence of Torsional Oscillations." By Professor Andrew Gray, F.R.S., and Alexander Wood, B.Sc., Houldsworth {esearch Student in the University of Glasgow. Received May 1,—Read May 15, 1902.
We can obtain information as to the nature of the magnetisation of magnetisable bodies only by testing the various hypotheses with reference to effects which it seems likely should, under these hypotheses, be produced on the physical properties of the substance. Thus, for example, the internal friction of the different parts of a solid must depend upon the size and mode of arrangement of these parts, and any alteration in their dimensions or relative arrangement ought in general to produce some change in the amount of the internal friction. Magnetisation of iron and other substances has with great probability been supposed to consist in a rearrangement and general alignment of the particles of the substance, already themselves elementary magnets, but so arranged in the unmagnetised metal as to be unproductive of any external magnetic field. It is not unusual to suppose that this unmagnetised state is one of what we may call complete absence of arrangement, and it is sometimes so represented in text-books on the subject of magnetism, where pictures are given of a perfectly confused distribution of elementary magnets, so completely mixed up as to have no preponderating magnetic moment in any one direction. Any such distribution, it is clear at once from the most elementary considerations, is impossible, as a large majority of the elementary magnets would otherwise have to remain in stable equilibrium in
