ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 601 



100 varieties ; it also shows their spectro-photometric absorption curves, 

 and also gives their percentage transmission. Some new filters are 

 introduced, inckiding a photometric set, an ultra-violet, and an infra-red. 



Photography of Coloured Objects.* — The second edition of this 

 work includes most of the matter included in the previous edition, 

 together with an incorporation of much of that contained in the 

 Wratten book on " Orthochromatic Filters." 



(5) Microscopical Optics and Manipulation. 



Drawing of Microscopic Preparations.f — A. Maillefer describes a 

 method of drawing microscopic images with the help of a reflecting 

 prism in a sort of dark chamber. The light from a Liliput electric lamp 

 after passing through a water-cooler traverses an aperture in the wall of 

 the dark chamber and falls upon the objective of the Microscope ; on 

 issuing from the eye-piece a totally reflecting prism projects the image 

 vertically downwards on to the paper placed on the working table. 

 The dark chamber is merely a light framework covered with opaque 

 black cloth, the whole being of such a size as to contain the instru- 

 ment and the operator. The cloth must be loose and so arranged as to 

 enwrap the operator completely and prevent light from entering the 

 chamber from any direction. Dimensions and details are fully given, 

 and the author expresses great satisfaction with the arrangement. 



(6) Miscellaneous. 



Optical Glass. I^W. Rosenhain, in his first Cantor Lecture on the 

 above, points out that the term " optical glass " should be used in such 

 a way as to mean a substance distinguished from even the best of 

 ordinary glass by a whole series of important properties, which can, 

 however, i3e summed up in two groups : (1) properties relating to 

 "general quality," in regard to which "optical glass" is simply a 

 " better quality " than ordinary glass ; and (2) properties of a more 

 specifically optical kind, relating to the refractive and dispersive powers 

 of the glass. Under the first head the subjects of transparency, colour, 

 devitrification, strite, interaction between the glass and the crucible, 

 internal strain, hardness, and durability, are discussed in a very instruc- 

 tive and interestiug way. Under the second head the lecturer treats 

 of refraction, dispersion, and the conditions necessary for achromatic 

 and apochromatic combination. 



The second lecture deals with the present modes of optical glass 

 manufacture, and gives the reader some insight into the physical and 



* The Photography of Colovired Objects, 2nd ed. Kodak, Limited, London^ 

 1916, 118 pp. (63 figs.). 



t Bull, de la Soc. Vaudoise des Sciences Naturelles, 11. (1916) pp. 1-7 (1 fig.). 

 t Journ. Roy. Soc. Arts, Ixiv. Nos. 3324-6 (Aug. 1916). 



Dec. 20th, 1916 2 T 



