320 The Microscope. 



For clearness of definition, marginal and central, for flatness 

 of field and freedom from color, both marginal and central, these 

 two eye-pieces are superior to anything I have ever looked 

 through. 



The marginal definition and correction, which is poor in the 

 ordinary run of oculars, is nearly perfect in these two eye-pieces. 



I have in my collection a ^ inch objective (never mind who 

 the maker is) in which the central definition and correction are 

 good, but the marginal poor. On using this objective with 

 these oculars I found a decided improvement in clearness of 

 definition and flatness of field, especially noticeable at the mar- 

 gins. 



The ^ inch gives greater magnification than my Spencer ^ 

 solid, and is superior in definition and flatness of field. 



The heartiest thanks and good wishes of microscopists are 

 due Mr. Herbert R. Spencer, of this city, for the production of 

 an ocular superior to any in the market to-day. 



John A. Miller, Ph. D. 



Niagara University, Buffalo, N. Y. 



Editor The Microscope : — 



I think it is in the last number of The Microscope that gela- 

 tine is recommended for the first ringing of balsam mounts. • I 

 have tried the method thoroughly, but have not found it really 

 satisfactory. About a year and a half ago I began using a thin 

 solution of collodion, following it with shellac, then finishing 

 with asphalt, and have found this entirely reliable and very con- 

 venient. The trouble with the gelatine has been a tendency to 

 crack, and that even with admixture of glycerine. The collo- 

 dion, on the contrar3f, is very tenacious, is hardened at once by 

 evaporation of its ether, and is, in turn, insoluble in the shellac. 

 I presume the shellac is not really necessary, as mounts finished 

 without it have stood perfectly well, but I use it as an addi- 

 tional precaution. 



I find that a mount with very fluid balsam may be closed at 

 once, and safely, without the wearisome dela}' entailed by bak- 

 ing. Yours truly, 



Albion, Mich. C. E. Barr. 



