344 "The Microscope. 



desired information. Prof. H. L. Smith's device is not obtaina- 

 ble, and that of the German optician can be had, I suppose, only 

 by buying one of his homogeneous immersion objectives. With- 

 out some such means, the microscopist can never know whether 

 he is getting the best work from the objective or not, unless he 

 attempt to resolve the proper Diatom every time he begins to 

 use a fresh supply of immersion medium, a method that would 

 be time-consuming, and should be unnecessar3\ While with the 

 improper fluid he may get moderately good results, with a med- 

 ium of the correct refractive index, he will get the best that the 

 objective can give, provided of course the lens be properl}' man- 

 ipulated. 



Mr. Herbert R. Spencer, (Spencer & Smith, Buffalo, N. Y.,) 

 is introducing a new series of homogeneous immersien objee- 

 tives at a moderate price, and intended, as the makers say, to 

 take the place of the cheap foreign objectives now becoming so 

 popular in this countr}^, and more than filling their place. The 

 objectives, by change of collar adjustment, correct for water, 

 glycerine and for homogeneous immersion fluid. They are said 

 to have a remarkably long working distance, and to resolve the 

 difficult tests in balsam with mirror illumination alone. I have 

 not seen any of these new lenses, but Mr. Spencer's word in refer- 

 ence to their good qualities is sufficient His work is always, and 

 in every way, exactly as is claimed by the accomplished workman. 



Spencer's improvement in e3^e-pieces, as recently mentioned by 

 Prof. J. A. Miller in The Microscope, merits attention by micro- 

 scopists that desire the best optical appliances in their efforts 

 to pry into things, but unfortunately the improvement cannot 

 be applied to an ocular below the one inch in power. The two 

 inch, so much used by all working microscopists, cannot be suc- 

 cessfully made by the improved method, by reason of the great 

 size of the component lenses ; no body-tube as now made is large 

 enough to receive the improved two inch eye-piece. Hitherto 

 comparatively nothing has been done toward the improvement 

 of the Huj'ghenian ocular. There is room here for some pro- 

 gressive optician to do good work that shall help himself and 

 microscopical science at the same time. There have been so- 

 called achromatic eye-pieces made in Europe, but they have 

 never come into general use, and have attracted little attention. 



