372 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



tion (fig. 06) the iris diaphragm has a scale marked above the slit, a 



tie 



c 



feature often of great convenience 



c t 



Fig. 66. 



J. E. Stead's Illuminator for Opaque Objects.* — This is a simple 

 and effective apparatus for illuminating me- 

 tallurgical specimens by reflected light, but is 

 only intended for use with low-power objec- 

 tives, 1^-3 in. The illustration (fig. 67) suffi- 

 ciently explains the principle of illumination. 

 The metal box has one of its sides cut at an 

 angle of 45°, this being faced with a small 

 square of glass, the surface of which is illu- 

 minated by means of a lamp with or without 

 the intervention of a bull's-eye condenser. 

 The circular collar pushes on to the body of 

 the objective. 



Fig. 67. 



Siedentopf & Szigmondy's New Microscopic Apparatus for rendering visible 

 Ultra-microscopic Particles in Glasses and Liquids. 

 [This apparatus is now made by C. Reicliert] 



C. Reichert (Vienna) Special Circular. 



(6) Miscellaneous. 



High Power Microscopy .f — In an address at the Royal Institution 

 J. W. Gordon observed that in the exhibition of a microscopic object 

 under high magnifying power there are three stages in which difficulties 

 have to be met and surmounted — (1) In the preparation of the object 

 for exhibition under suitable conditions of illumination ; (2) in the 

 representation of the object by means of an image ; (3) in the trans- 

 mission of the image so found in the instrument to the eye of the 

 observer. Professor Wright classified the preparation of objects into 

 colour pictures by means of stains and outline pictures. The method of 

 staining having manifest limitations, Mr. Gordon proceeded to refer to 

 the use of cross-lighting or " dark-ground illumination " in order to show 

 outlines, with especial reference to Dr. Siedentopf's application of this 

 principle to the exhibition of so-called " ultra-microscopical particles." 



* J. Swift and Son's Catalogue (1904) p. 35. 

 + Knowledge, ii. (1905) pp. 114-15. 



