Page:On a Self-recovering Coherer and the Study of the Cohering Action of different Metals.djvu/7

172 glass vessel filled with kerosene, through which no ultra-violet light could have been transmitted. To put the matter to final test, I lighted a magnesium wire in close proximity to the receiver without producing any effect. Thick blocks of wood of ebonite and of pitch were interposed without checking the action. I then used polarised electric radiation, and interposed a book analyzer, 6 cm. in thickness; when the analyzer was held parallel, there was a vigorous action, but when it was held in a crossed position all action was stopped. No visible or heat radiation could have been transmitted through such a structure, and there can be no doubt that the action was entirely due to electric radiation.

It would be interesting to investigate whether the observed action of electric radiation on a potassium receiver is in any way analogous to the photo-electric action of visible light. I have commenced an investigation on this subject, the results of which I hope to communicate on another occasion.

 

(Abstract.)

In a previous communication, read to the Society on March 16, a preliminary account was given of some of the results the authors had arrived at in studying metals by the microscopic methods initiated by Sorby, and pursued by Andrews, Arnold, Behrens, Charpy, Osmond, Roberts-Austen, Stead, and others. The present paper deals with a development and extension of the same work. It relates chiefly, though not exclusively, to the effects of strain, and the relation of plasticity to crystalline structure.

It is well known that the etching of a polished surface of metal reveals, in general, a structure consisting of irregularly shaped grains, with clearly marked boundaries. Each grain is a crystal, the growth of which has been arrested by its meeting with neighbouring grains. This view, as Mr. Stead has pointed out, is strongly supported by the appearance of the etched surface under oblique illumination, when the several grains are seen to reflect light in a way which is consistent only with the idea that on each there is a multitude of facets with a definite orientation, constant over any one grain, but different from grain to grain. The formation of such a structure is well exhibited, on a relatively enormous scale on the inner surface of a cake of solidifying 