NOTES AND MEMORANDA. 269 



with binocular microscopes." The arrangement proposed by Dr. Ward 

 will undoubtedly work as he proposes, but cui bono ? It is an axiom 

 in microscopy, as well as in other pursuits, that the simplest means of 

 accomplishing an end is the best. Dr. Ward's arrangement is compli- 

 cated and troublesome, and unless all the lenses are well made and 

 carefully centred, definition will be injured. Dr. Ward is correct in 

 his observation that the " erectors usually furnished [italics are his] are 

 not good, and the use, otherwise satisfactory, of a good objective as an 

 erector has not yet afforded the advantage of binocular vision." The 

 first clause is correct, because " the erectors usually furnished " reverse, 

 counteract, or destroy all the corrections which the opticians have 

 taken so much pains to introduce into the objectives. The second 

 clause refers to binocular vision. This has been completely accom- 

 plished by Tolles' binocular eye-piece, which has been in use and 

 before the public more than six years. Without any change from, or 

 addition to, its regular construction or use, it gives an image erect, 

 binocular, and stereoscopic with any objective, from a 4-inch to a 

 ^-inch ; and of coiu'se it may be used for dissecting by transmitted 

 or reflected light with any objective having " working distance " 

 enough for manipulation — certainly with a ^-inch. The only objection, 

 if it is one, against the instrument for this use, is that the " power," 

 the amplification, is necessarily higher than with other binoculars. 

 But where a very loio power is wanted, I believe a pair of spectacles 

 set with magnifying periscopic lenses will prove to be better than any 

 binocular dissecting microscope yet devised. But the objection to 

 the " usual erector " for monocular instruments remains. This was 

 remedied by Tolles years ago ; so long ago that he has forgotten when. 

 He made erectors that did not disturb any of the corrections of the 

 objective, but preserved them, and gave as good effects as were 

 obtained without an erector. 



A Note on the above Remarks, which we suppose to be by Dr. Ward, 



and which is signed E. H. W., says that it can hardly be necessary to 

 state that Tolles' binocular eye-piece, with which the writer has some- 

 times worked, was ignored in the paper referred to, simply because there 

 was no occasion to mention it, — it being no novelty, but an article 

 whose properties have been perfectly familiar to American (and 

 foreign) microscopists for years. It is only fair to add that the new 

 arrangement, which can be added to any microscope at a cost of two 

 or three dollars, has been used for months by several microscopists, 

 who consider it extremely simj^le and convenient. That an erector 

 (or anything else), however perfect, can be added to the objective and 

 ocular, and give " as good " optical effects as would be obtained with- 

 out the additional refracting and dispersing sui'faces, is much disputed, 

 and surely cannot be considered a conceded point at the present time. 

 If Mr. Tolles is prepared to supply the market with erectors radically 

 superior to those generally used, microscopists will doubtless learn the 

 fact when it is announced, as he, E. H. W., does not find it now, in 

 the catalogue of the Boston Optical Works or in their advertisements 

 in the ' American Naturalist ' and other journals. 



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