ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 227 



2. The possibility that such deformation may be produced by 

 mechanical stress as arising from the possession of a certain amount of 

 rigidity by such solutions. 



S. The analogy between the effects so produced, and the double 

 refraction due to a magnetic field. 



Maillabd, L.— Le Loi de la Refraction et le principe de la moindre action. 



[An interesting historical review of the theories of refraction.] 



Bull, de la Soc. Vaudoise des Sci. Nat. (Lausanne), xli. 

 (Sept. 1905) pp. 173-95 (7 figs.). 



Munsbll, A. H. — On a Scale of Colonr- Values and a new Photometer. 



Technology Quarterly, xviii. (1905) pp. 60-72 (10 figs.). 



Rohs, von M. — Die Optischen Instrumente. 



Leipzig : B. G. Teuhner (1906) v. and 130 pp. 

 Schneider, J., & J. Just — Ultramikroskopio der Oleosole. 



[On the application of ultramicroscopy for testing the purity of oils and 

 oleaginous mixtures.] Zeitschr. Wiss. Mikrosk., xxii. 



(1905) pp. 481-530. 

 Thorp, T. — Replicas of Diffraction Gratings. 



Nature, lxxiii. (1905) p. 79. 



Wallace, R. J. — Ditto. Astrophysical Journal, xxii. No. 2. 



See also Nature, lxxiii. (1905) p. 21. 



Zsigmondy, R. — Zur Erkenntniss der Kolloide . Ueber irreversible Hydrosole und 

 UTtramikroskopie. (An account of the nature and properties of colloid solutions 

 or hydrosols, and of the investigation by the method of ultramicroscopy.) 



Jena: Gustav Fischer (1905) vi. and 185 pp. 



(6) Miscellaneous. 



Advances in Microscopy : The Microscope at Work.* — J. W. 

 Gordon dealt first with the subject of metallography, which he traced to 

 Dr. Sorby's work in Sheffield in 1864, illustrating its use in engineering 

 by a number of lantern slides lent for the purpose by Mr. J. E. Stead, 

 F.R.S., exhibiting the microscopic structure of steel. 



From this topic an easy transition served to introduce the subject 

 of the changes which the surface of a polished piece of metal undergoes 

 in the process of polishing. This part of the lecture was illustrated by 

 photographs lent by Mr. G. Beilby, of Glasgow, who has made a special 

 study of the physical condition of metals as affected by heat, and par- 

 ticularly by the treatment which they undergo in the polishing process. 

 His inquiries show that enormous forces, comparatively speaking, are 

 brought to bear upon the exquisitely thin film of metal which is directly 

 affected by the polishing operation in the act, for instance, of knife 

 cleaning ; and as the result of the hard usage to which this surface film is 

 subjected it carries permanent traces of having been spread like a fluid 

 over the solid foundation of underlying metal. A very remarkable 

 series of photographs illustrated this point, and showed how a polishing 

 tool left the surface of a piece of brittle metal like antimony in streaks 

 like the brush marks of paint. 



The next topic dealt with was the application of the Microscope to 

 the healing art — and here the lecturer selected for special notice the 



* Lectures at the Royal Institution, Feb. 1906. 



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