ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 461 



(3) Illuminating; and other Apparatus. 



Watson and Sons' New Objective Changer. — This apparatus 

 (fig. 69) was exhibited at the May meeting, and is fully described in 

 the Proceedings of the Society (see ante, p. 382). 



Fig. G9. 



Fedorow, E. von — Einigeneue Hiilfsapparate fur das polar isationsmikroskop. 



Ann. Geol. et Miner, de Russie, iv. (1901), p. 142 ; 

 Zeitschr. Krystallogr.,xxx\ii. (1903) p. 413. 

 Metcalp, M. M. — An electric lamp for Microscope illumination 



Science Notes.xv. (1902) p. 937. 

 Patterson, W. L.— A new changing nose-piece. 



Journ. Applied Micros., vi. (1903) p. 2162. 



Schmidt, H. — Ueber projections-nnd Vergr5sserungsapparate. 



Centraheitg. Opt. u. Mechan., xxiii. (1902) pp. 253, 265. 



(4) Photomicrography. 



Photomicrography of Rock Sections.* — This is one of the most 

 interesting applications of the Microscope, says W. Forgan, and one to 

 which, so far as can be learned, not much attention has been paid in 

 photographic literature. The sections of rocks are so varied in their 

 character that to very few of them can the same mode of lighting and 

 illumination be applied. It may be stated generally that granite and 

 its three components, quartz, felspar and mica, form the basis of all 

 rocks. Many other chemical substances assist in giving character and 

 variation in a greater or less degree ; but the three components of 

 granite are the ruling features in the whole of them. The chief use 

 of the photography of rock sections may be said to be the production 

 of lantern slides for teaching purposes. A good negative when repro- 

 duced in this way most materially assists in the illustration of a 

 geological lecture. In fact, to a class, or in a lecture of a more 

 popular form, such asssistance has now become indispensable. In the 

 production of negatives from rock sections it is, with few exceptions, 

 only necessary to use low magnifications. Only the other day a section 

 of rock was asked to be photographed, having an elliptical shape, the 

 major axis of which was over an inch in diameter. As no micro low- 

 power objective covers more than £ in., recourse was had to a Zeiss 

 Unar of 4|-in. focus stopped down to /ll, and this gave a very fine 

 sharp negative. The Microscope portion of the camera was removed, 

 and a supplementary stage on an improvised suitable rigid easel was 

 used to carry the section. Another method used for a different material 



* Brit. Journ. Photography, li. (1904) p. 489. 



