240 



THE AMERICAN MONTHLY 



[Dec. 1881. 



MICROSCOPICAL SOCIETIES. 



ILLINOIS STATE (CHICAGO). 



The semi-annual meeting was held on 

 Friday evening, October 28th, the Presi- 

 dent, Dr. Curtis, in the chair. Dr. Mer- 

 cer described and exhibited a camera 

 lucida by Nachet, of Paris, which dif- 

 fers considerably from those usually seen 

 in this country. It is a square prism with 

 its ends cut at an angle of about forty- 

 five degrees. It is so mounted that one 

 end is directly over the eye-lens of the 

 ocular, and this end is provided with a 

 smaller ninety degree prism, so mounted 

 that the pencil of rays from the ocukr 

 passes directly upward to the eye without 

 suffering any change of direction. The 

 two forty-five degree faces of the prism 

 serve to reflect an image of the pencil to 

 the eye of the observer, thus reversing the 

 performance of the ordinary camera, 

 which changes the direction of the rays 

 from the object under examination. Dr. 

 Mercer thought the apparatus had some 

 qualities which entitled it to consideration, 

 the ease with which it could be used by 

 an inexperienced person being a strong 

 recommendation. In reply to Mr. Bul- 

 lock, he stated that it could be used with 

 as high as a two-thirds-inch ocular, pos- 

 sibly with one of still higher power. 



Dr. Johnson exhibited a high-angled }i 

 objective, made by Powell & Leland. Its 

 balsam -angle was forty degrees, and the 

 makers claimed that it would resolve the 

 Amphtpleura ^elhicida into beads. It 

 had agood working-distance, and, although 

 an oil-immersion, it could be used with 

 glycerin and probably with water. It 

 had a remarkably flat field and compared 

 favorably with a Zeiss ^^ in his posses- 

 sion. 



An immersion-condenser came with the 

 objective. It is quite different from the 

 ordinary high-angled condenser made by 

 this firm, and consists of two systems of 

 lenses, placed close together, the lower of 

 which is very large, the upper very small. 

 The pencil of rays, therefore, has a high 

 angle of convergence, probably as much 

 as one-hundred and fifty degrees for bal- 

 sam. It is provided with a diaphgram 

 with central and side apertures, the latter 

 at an angle of ninety degrees. It has also 

 a pin-hole aperture for centering. 



A Powell & Leland cobweb microme- 

 ter was also exhibited by Dr. Johnson, 

 E. B. Stuart, Secretary /rtf/^;«. 



u 



Exchanges. 



[Exchanges are inserted in this column without 

 charge. They will be strictly limited to mounted 

 objects, and material for mounting.] 



Mounted slides of Selenites for the Polariscope, in 

 most beautiful and brilliant colors, in exchange for 

 first-class Histological and Pathological slides and 

 slides of diatoms, algae, etc., 



A. C. GOTTSCHALK, 

 193 North Salina Street, Syracuse, N. Y. 



Unmounted objects, Foraminifera, Spicules, Zoo- 

 phytes, etc., in exchange for other objects, mounted 

 or unmounted. E. PINKNEY, Dixon, 111. 



Unmounted objects, Foraminifera, Spicules, Plant- 

 hairs, Zoophytes, etc., in exchange for other objects, 

 mounted or unmounted. 



E. PINCKNEY, Dixon, 111. 



Wanted — First-class mounts of double-stain vege- 

 table preparations in exchange for first-class insect 

 preparations. H. S. WOODMAN, 



P. O. Box 87, Brooklyn, E. D., N. Y. 



Well-mounted Histological and Pathological slides 

 in exchange for other first-class slides. 

 W. H. Bates, M.D., 184 Remsen St. Brooklyn, N. Y. 



Wanted — first-class prepared and crude material, or 

 mounted objects, in exchange for diatoms in situ or 

 other first-class crude material, or for mounted objects. 

 M. A. BOOTH, Longmeadow, Mass. 



Niagara River Filterings for mounted slides. 



H. POOLE, Buffalo, N. Y. 



Wanted — good gatherings of Diatoms, fossil or re- 

 cent, especially of test forms. Liberal exchange in fine 

 slides : prepared or rough material. Lists exchanged. 



C. L. PETICOLAS, 635 8th Street, Richmond,Va. 



Good, uncleaned Diatomaceous material containing 

 A rachnoidiscus^ Heliofielta^Plenrosig7>ia^ Isthniia, 

 Triceratium, Surirella geinnia and Terpsinooe^ 

 tnusica wanted, in exchange for well-mounted slides 

 of arranged diatoms, etc., or cash. 



DANIEL G. FORT, Oswego, N. Y. 



Well-mounted Histoloj^ical and Pathological slidesy 

 in exchange for oiher ^rst-class slides. 



LEWIS M. EASTMAN, M. D., 

 349 Lexington Street, Baltimore, Md. 



For exchange : Mounted thin sections of whale- 

 bone, soapstone, serpentine, albite, feldspar, etc.;. 

 also opaque mounts of several very beautiful fossil- 

 iferous limestones. 



Rev. E. A. PERRY, Quincy, Mass. 



Well-mounted, typical Pathological and injected 

 Histological preparations, in exchange for other well- 

 mounted slides. Diatoms, Algae and Fungi preferred. 

 HENRY FROEHLING, 

 59 N. Charles Street, Baltimore, Md. 



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