294 Prof. A. Gray and Mr. A. Wood. Effect of a [May 1, 



12. 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. 



13. By this method, invisible traces of physico-chemical change in a 

 wire may be detected. 



14. Chemical reagents not only change the excitability but the 

 quickness of response. Two points having two different rates of exci- 

 tation will thus, under proper conditions, give rise to diphasic effects. 



I take this opportunity to thank the Managers of the Boyal Insti- 

 tution 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 Bate of Subsidence of Torsional Oscillations." By 

 Professor Andrew Gray, F.B.S., and Alexander Wood, 

 B.Sc, Houldsworth Besearch Student in the University of 

 Glasgow. Beceived May 1,— Bead 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 hypo- 

 theses, 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 



