92 



THE AMERICAN MONTHLY 



[May, 



f 



when putting public money into the 

 hands of private persons. 



' The new furnace was lighted in 

 September, 1884, and since that time 

 Dr. Schotthas been actively engaged, 

 almost day and night, in overcoming 

 the difficulties of the operations. 

 The experiences of other manufactur- 

 ers being inaccessible to a new com- 

 petitor, everything had to be learned 

 anew. A year later the first part of 

 the matter was brought to an end — 

 the production of the ordinary sili- 

 ceous glass, and this, since last 

 autumn, is used by nearly all German 

 opticians. In a few months, it is 

 hoped that the borates and the phos- 

 phates will also admit of regular pro- 

 duction, and then the Jena manufac- 

 tory will be opened for the supply of 

 optical glass on a strictly scientific 

 basis. 



' This extension of the work has 

 had the eflect of delaying the intro- 

 duction of better glass into micro- 

 scopical optics by more than two 

 years. In the summer of 1883, suf- 

 ficient materials had been obtained 

 for the construction of microscope- 

 lenses, and, in fact, the first objectives 

 were made by Messrs. Zeiss at that 

 period, but after it had been decided 

 to establish a manufactory with the 

 aid of public money, Messrs. Zeiss 

 were obliged to abstain from using 

 the new glass, and to wait until the 

 latter should be accessible to other 

 opticians also. 



' At present the objectives are not 

 on sale, but it is expected that very 

 shortly both objectives and glass can 

 be purchased in the usual way.' 



Photo-Micrograpliy. — YI. 



BY THE EDITOR. 



\_Contitmed from f. 70. ] 



4. Developing. 



In continuation of this part of the 

 subject we proceed to describe the 

 process of developing an exposed 

 plate, with the ferrous oxalate devel- 

 oper, after which the pyrogallic acid 



or so called pyrodeveloper will be 

 considered. 



a. Fen-Oil s oxalate develop- 

 meiit. 



This developer has always been a 

 favorite one with us, because it 

 works so clean, and gives negatives 

 free from color. Many writers af- 

 firm that it is not equal to pyro in 

 bringing out details on a plate, par- 

 ticularly if the exposure has been 

 insufficient for the subject. We can 

 only say in reply to such statements 

 that if a plate has been exposed long 

 enough to give a picture of any 

 value, it can be developed perfectly 

 well with ferrous oxalate, and when 

 the ferrous oxalate will not develop 

 the details, an attempt to bring them 

 out with pyro will result in a fogged 

 plate. Such a proceeding is never 

 to be advised, for a plate not suffi- 

 ciently exposed cannot yield a good 

 picture by developing with a strong 

 developer. In passing, however, it 

 may be remarked that this is pre- 

 cisely the course recommended by 

 many writers in the photographic 

 magazines — a course fatal to success 

 in every case. 



That the beginner may know when 

 the exposure has been about right it 

 may be said that in a properly ex- 

 posed plate the picture develops 

 slowly, and gradually increases in 

 strength while the contrasts betsveen 

 light and dark parts are decided, and 

 as clear as in the subject. If the 

 white parts become covered and the 

 plate looks iis though it was devel- 

 oping all over at once, it is an indica- 

 tion of over-exposure, and the begin- 

 ner would do well to discard it and 

 repeat the exposure. Sometimes 

 beginners try plate after plate and 

 fail to get good pictures, and cannot 

 understand the reason for such fail- 

 ures. Usually the fault is in expos- 

 ing too long. A good way to get 

 the proper time is to draw the dark 

 slide say one-third out and expose 

 about one second, then draw it a 

 little further out and expose another 

 second, then draw it entirely out and 



