loo 



SUMMAEY OF CURRENT RESEARCHES RELATING TO 



.(3) that perfect adjustment of condenser with Microscope, even if set 

 up, is exceedingly difficult to maintain. It would be interesting to know 

 on what optical grounds it could be proved that a method of centring 

 the objective in relation to an eye-piece and substage, which are them- 

 selves not in alignment, could be justified. Hence the English Micro- 

 scope is supplied with centring screws to the substtige. 



The statement that instead of a mechanical draw-tube the Continental 

 maker provides his objective with coriection collars, seems to imply that 

 correction collars are unknown to English manufacturers. Yet, as 

 Barnard points out, Powell and Lealand fitted correction collars to their 

 objectives some seventy years ago, and have continued to do so. More- 

 over, every English house does the same. 



As to the want of uniformity in tlie Royal Microscopical Society 



standards, the original author has 

 a fair cause for complaint. At the 

 same time it must be pointed out that 

 the chief cause of variability is not 

 that the Society's standards are wrong, 

 but that makers, whether English or 

 Continental, have failed to conform to 

 them. Although the Society has been 

 for some time considering these stand- 

 ards, and has a sub-committee even 

 now dealing with the subject, there is 

 no doul>t that it would welcome the co- 

 operation or assistance of the National 

 Physical Laboratory in the matter, as 



(^_,. I ^'^ '^ '^"^ ""^^ without difficulty, and the 



^M j 11 greater the weight of opinion which 



— ^■' - - J. yJ could be brought into combination the 



better. 



(3) Illuminating- and other Apparatus. 



Petrol-vapour Incandescent Gas 

 Lamp.* — The container of this lamp 

 (fig. 18) is filled with petrol ; the burner 

 is warmed by means of a small spirit 

 lamp, and the light is obtained by the in- 

 candescence of a mantle. The light is 

 brilliant and actinic and is easily con- 

 trolled. It is recommended for photomicrography dark-ground con- 

 densers, etc., where gas and electric light are not available. 



Reichert's New Universal Projection Apparatus.!— 0. Heimstiidt 



descril)es this apparatus, which was intended by its designers to possess 

 in the highest degree— (1) complete security of apparatus, (2) extreme 

 simplicity and light-strength in episcopic, and (3) diascopic projection 

 ..._,i ^ n_ , rpj^^ realization of the first object is evi- 



FiG. 18. 



under strong magnification. 



* Watscn's Special Catalogue, 1912. 



t Zeitschr. wiss. Mikrosk., xxviii. (1911) pp. lGl-74 (G figs.). 



