A letter from Prof Bailey to
West Point, NY, Nov 27, 1847
The American Journal of Science
Having carefully examined an achromatic microscope made for Dr. Gilman by Charles A. Spencer, Esq., of Canastota, N.Y., I can with confidence as well as pleasure, give my testimonial to its great excellence. I have had it side by side with my own large microscope, (one of Charles Chevalier's largest achromatics, price 1000 francs), and can speak unhesitatingly of their relative merits. I have used Chevalier's instrument with great satisfaction for several years, and have found it in almost every respect convenient and satisfactory. In regard however to the lenses of higher power, it is a fact easily established by comparative trial, that Spencer's lenses are far superior to any of Chevalier's which I have yet seen. Its superiority consists in a great angle of aperture and much better definition. With Spencer's glasses I was able, without difficulty, to see the cross lines on the Navicula hippocampus, (the most difficult test object now known to me, and which was sent to me from England, as the test object par excellence, while with Chevalier's, by the same light, I could see them only with great difficulty. I do not think Spencer's microscope quite equal to the far more expensive English ones by Ross or Powell, and I cannot positively assert that it is superior to the best of those made by Oberhauser or Ploessels, as I have not had an opportunity to compare them properly side by side in the same light; my impressions however are that in the microscope made by Mr. Spencer for Dr. Gilman, is in no respect inferior to any of Oberhauser's that I have seen, and I am by no means certain that it is not superior. I certainly had a better view by candle light of the transverse lines of the N. hippocampus, by means of Spencer's instrument, than I was able, subsequently, to to by daylight by means of Oberhauser's. As a proof of the great excellence of Spencer's lenses, I will state that with them, I was not only able to find difficult lines whose existence I was aware of, and for which I was seeking, but on some objects, lines of whose existence I had no suspicion, came out so as to force themselves on my attention. I look upon the results obtained by Mr. Spencer as a proud triumph for American art.
Prof. of Chemistry, U.S. Military Academy
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