114 



SUMMARY OF CURRENT RESEARCHES RELATING To 



20. On improvements of the Microscope by means of new kinds of 



optical glass (1886). 



21. On the effect of illumination by means of wide-angled cones of 



light (1889).* 



22. On the adaptability of fluorite for optical purposes (1890). 



Focussing Safeguard.! — In showing microscopic objects to those 

 unacquainted with the use of a Microscope, there is always the risk of 

 accidental injury to either the slides or objectives when the latter are 

 of short focal length. To obviate risk of injury S. E. Dowdy has 

 devised the following contrivance (fig. 1G). A B is a metal collar, 

 velvet lined, with a screw at A for clamping on to the objective. 

 D is a fine screw rotating with arm B C, and having a felt-covered 

 circular base, E. In use, the objective should first be accurately 



Fig. 16. 



focussed, and then by means of the fine adjustment brought within 

 its focal length, with its front lens as near as possible to the cover-glass 

 without touching it. 



The screw D is then rotated until the base touches the slide, when it 

 will be obvious that it would be impossible to bring the objective into 

 contact with the cover, though focussing in a safe direction may be 

 effected to any extent. 



Ultra-Microscopic Investigation of Colour-matters and their 

 Physiological Significance.! — A. Birch-Hirschfeld describes howBaehl- 

 mann used a new Microscope, introduced by Siedentopf and Zsigmondy, 

 of Jena, which, by means of a brilliant focal, lateral illumination, renders 

 visible the smallest particles (5/a to 10//) in their natural colour. With 

 this instrument he examined solutions of colouring matter, such as 

 Prussian-blue, carmine, ultramarine, naphthol-yellow, and so forth. The 

 resolution of each of the colouring matters into its component colours 



* Journ. E.M.S., ix. (1889) pp.721-4. 



t English Mechanic, lxxviii. (1903) p. 291 (1 fig.). 



X Ophth. Klinik, Aug. 20 and Oct. 5, 1903. See Ophthalmoscope, i. (1903) p. 21 8. 



