ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 489 



improvements, and the new form of the instrument has certain advan- 

 tages which he considers adapt it for undertaking the most difficult 

 tasks in the best way. 



His Microscope-table is intended to give facilities for the ready 

 photomicrography of any important detail when found, and for the 

 immediate resumption of subjective observations. He gives full details 

 of both pieces of apparatus. 



Obtaining Density in Photo-micrography.* — One of the chief 

 difficulties, says C. F. Emeny, met with in photomicrography is — judging 

 from the number of weak examples one sees, the product evidently of 

 thin negatives — the securing of sufficient density in the negative so as 

 to yield a print showing enough of contrasts to produce a pleasing 

 effect ; and in this article it is proposed to attempt to show how 

 improvement may be secured. Let it be understood, however, that 

 mechanical and microscopical conditions are assumed to be correct, and 

 that only the photographic aspect is being considered. 



Lack of density may be due to several causes, such as under-exposure, 

 unsuitable developing agent, or unsuitable brand of plate — especially 

 the use of a non-orthochromatic plate on an object more or less yellow 

 in colour or put up in a more or less yellow medium. By the use of 

 an orthochromatized plate of medium speed such as the " Imperial Non- 

 filter," density is easily obtainable, always provided that sufficient 

 exposure is given to allow the developer to give a good deposit of 

 reduced silver in the film. 



The choice of a suitable developer is a very important factor, and to 

 the use of an unsuitable one may be ascribed much of the " lack of 

 density " trouble. Amateur photographers are, from text-books and 

 other sources, led to believe that the process of development is more or 

 less automatic ; but, while this may be to some extent true, it yet 

 remains a fact that negatives of the requisite contrast and density are 

 much more likely to be secured if thought is expended and care em- 

 ployed in the selection and use of a developer that will give the result 

 sought for. 



Two plates of the same subject and with identical exposures can yet 

 be made to produce widely differing results — one a flat, dead picture, 

 and the other a print full of brilliance and life, and this simply by the 

 use of different developers. Metol-Hydroquinone developers (M.Q.) 

 should never be employed where negatives giving brilliant results are 

 desired ; but the pyro-soda developer will be found much more satis- 

 factory for the purpose, and if it is compounded according to the 

 appended formula will be found to be practically non-staining. 



Pyro-soda gives a negative having a deposit of far greater light- 

 stopping properties than does the M.Q., and if two plates are developed 

 to the same degree of visual intensity — one with each developer — the 

 pyro-developed negative will be found to give a much more brilliant 

 print tlian the other owing to the yellower and less actinic colour of the 

 deposit in the film (quite apart from any question of stain) ; the M.Q. 



* Journ. of Micrology, 1914, pp. 57-8. 





