ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
545 
In the two succeeding chapters examples are given of the application of 
the methods upon cylindrical and spherical objects belonging to the 
vegetable kingdom, such as starch-granules, &c. The subject of pleo- 
chroism is then touched upon, and lastly a brief description is given of the 
methods of investigation in convergent light. 
(2) Eye-pieces and Objectives. 
Spencer & Smith’s Aplanatic Eye-piece.* — Dr. M. D. Ewell writes : — 
“ I have recently purchased from Spencer & Smith, of Buffalo, N.Y., a 
1 in. positive eye-piece, which is so far superior to anything I have 
ever before used (and I have a large assortment), that I feel justified in 
calling the attention of microscopists to it. In common I suppose with 
the majority of workers, I, for a long period, paid no special attention 
to my eye-pieces, which, however, happened to be good ones, but centered 
my attention upon the objective and stand. I have long supposed that 
no available use could be made of any eye-piece for the micrometric 
purposes except in a limited portion of the centre of the field, never 
exceeding one-half thereof. 
With the eye-piece in question I find sensibly equal amplification 
and no distortion, almost to the extreme edge of the field. In this 
respect it far surpasses the Ramsden and Huyghenian eye-pieces. 
I find also that with it the definition, which I always test on a 
podura, is much improved, and that it is good almost to the extreme 
edge of the field, and this without any new adjustment of the focus. 
Altogether this eye-piece, which for want of a better name I shall call 
“ Spencer & Smith’s Aplanatic Eye-piece, 5 ’ is in my judgment a distinct 
advance over existing eye-pieces. I have ordered another one for my 
Zentmayer filar micrometer, and propose to use it hereafter in my micro- 
metrical work in preference to those heretofore used.” 
New Objectives.! — Mr. H. L. Tolman remarks : — “ Among the new 
objectives recently made which are deserving of note are two, a 1/5 
and 1/8 both dry, of 150°, by Spencer & Smith, or as the firm used to 
be known, H. R. Spencer & Co., of Buffalo. These objectives are on a 
new formula, and for flatness of field, freedom from colour, and sharp 
definition they rank very high. In fact the robust images they give so 
much resemble in character those of the Zeiss apochromatics that they 
would be indistinguishable. They work easily through a No. 2 cover, 
and of course have cover correction. Perhaps I am rather an enthusiast 
in favour of Spencer’s work, but without prejudice to any one else, I say 
without hesitation, I never have seen better dry glasses than these. I 
believe there is none of the Jena glass used in them, but the chromatic 
aberration is most exquisitely corrected, and it is gratifying to know 
such correction can be made without the necessity of using the as yet 
unproved kinds of glass.” 
Magnifying Power of Objectives.! — Mr. H. L. Tolman offers the 
following remarks on this subject : — “ The question of how much a given 
objective will magnify has always been an important, but difficult one to 
answer, and every assistance offered toward solving it is worthy of atten- 
* Amer. Mon. Micr. Journ., xiii (1892) p. 103. f Tom. cit., p. 98. 
X Tom. cit., pp. 93-4. 
1892. 2 p 
