172 



Prof. J. A. Ewing and Mr. W. Bosenhain. 



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 inter- 

 posed 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 in- 

 vestigation on this subject, the results of which I hope to communicate 

 on another occasion. 



Bakerian Lecture. — " The Crystalline Structure of Metals." By 

 J. A. Ewing, F.B.S., Professor of Mechanism and Applied 

 Mechanics in the University of Cambridge, and W. Bosen- 

 hain, 1851 Exhibition Besearch Scholar, Melbourne Univer- 

 sity. Delivered May 18, 1899. 



(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, 

 Boberts-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 rela- 

 tively enormous scale on the inner surface of a cake of solidifying 



