^■* -*i> n 



:i 



^ 



■ 



, . ' On Microscopes and Microscopy. 61 



foi^ their object appears to have been to combine the greatest sim- 

 plicity with working qualities. 



This is very desirable because it insures several other import- 

 ant conclitionsj not to mention an incomparable cheapness, thus 

 bringing them within the means of any one who would study 

 this subject; it makes them portable, easily rigged, and not at all 

 liable to derangement with the longest journeyings. But while 

 Isay this, let me if5d; that I think the mounting is rather too 

 1^ simple — in other words, I think it might be so ahered, or have 



additions, that would increase its power of showing the capabili- 

 ties of lenses, at the same time not infringing upon its working 

 qualities. (Let me here say in parenthesis, that both M. Ober- 

 hauser and M. Nachet are now directing their attention to this 

 pomt.) I have here referred' /only to their mountings j their 

 lenses have peculiarities worthy of notice. From what has been 



f said, you will perceive that I do not think the French lenses 



equal either to the English or to those of Mr. Spencer. In work- 

 ing them they have sought every way to give them ordinary 

 working qualities, their angles of aperture are narrow, which in- 

 sures a long focal distance and di flatness of field not often seen in 

 other instruments. This is particularly true of those of M. Ober- 



^ haussr, and combined with his platine tournante^ is the cause of 



• his well-merited success. 



This class of instruments have certainly done more than any 

 other for building up microscopical science, (which is not made 

 up of the study of test-objects.) For working qualities upon 

 ordinary objects, and particularly in many departments of natu- 

 ral history and pathology, requiring the use of from 300 diame- 

 ters to quite low powers, they are very desirable, and answer the 

 purpose of most other instruments with but half the cost.* 



There are very many people who have a taste for pursuing 

 niicroscopic studies, but it is not all of these who would like to 

 loUow the subject into all its most intricate departments; ihey 

 would prefer to be pilgrims to a certain extent in the paths others 



^ before them have made, rather than pioneers on unbeaten tracks; 



such do not require the very best insnaiments. 



It appears to me that those who wish to go beyond present 

 niicroscopy, and investigate points of a very doubtful nature, will 

 Jjot succeed perfectly with the lenses of Oberhauser or Nachet. 

 Not only because their high powers lack a sharpness of defini* 

 ^ion, but because their powers are not sufficiently high for such 

 studies. Oberhauser's highest power is 800 diameters, Nachet's 

 1100. And even with these the darkness of the field causes 

 them to be seldom used; and I have found these powers not ad- 



**^ 



«lL-. 



^•' t^»«jui in uwi, a— "rtion. 1 rn;iv raonuon tnai i suw on in- vfi»viiKiu-ui o w/w*o, 

 ^ore orders for iiistrumcBt:, tiom Loudou iUid other hax'^v cine:* of Great Britain 

 tnan elsewhere^ » • fit 



|£ • ' ■ ^ # 



^ 



# 







