THE MICROSCOPE. 159 



THE semi-annual meeting of the State Microscopical Society of 

 Illinois was held at the Academy of Sciences, 263 Wabash Ave.» 

 on Friday evening October 28th. The President, Dr. Curtis, in the 

 chair. 



The minutes of the previous meeting were read and approved, 

 and the usual routine business transacted, after which Dr. Mercer 

 described a camera lucidia by Nachet of Paris, which differs con- 

 siderably from those usually met 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 ocu- 

 lar, and this end is provided with a smaller ninety degree prism, so 

 mounted that the pencil of rays from the ocular 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 per- 

 formance 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. Bullock he stated 

 that it could be used with as high as a two-thirds inch ocular, possi- 

 bly with one of still higher power. The cost of the apparatus was 

 stated to be 14 f. 



Dr. Johnson exhibited a high angled one-eighth objective made 

 by Powell & Leland. Its balsam angle was +140° and its makers 

 claimed it would resolve the amphipleura pellucida into beads. It 

 had a good working distance, and although an oil immersion, could 

 be used with glycerine and probably with water. It had a remark- 

 able flat field and compared favorably with a Zeiss one-twelfth in 

 the speakers possession. An immersion condenser came with this 

 objective. It is quite different from the ordinary high angled con- 

 denser 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. Its pencil of rays therefore has a high angle of conver- 

 gence, probably as much as 150° for balsam. It is provided with a 

 diaphragm with central and side apparatus, the latter at an angle of 

 ninety degrees. It has also a pin-hole aperture for centering. A 

 Poweli & Leland cob-web micrometer was exhibited by Dr. John- 

 son. 



E. B. Stuart, 



Secretary pro tem. 



