1871.] 347 [Bicknell. 



camera lucida, at an angle of 30° from horizontal, a perfect 

 view of objects on the stage of the microscope is obtained. 

 The position is thus very easy, and entirely free from the 

 usual constraint attending the use of the microscope when in 

 a vertical position. 



Mr. Bicknell also exhibited an achromatic condenser made 

 in the form of an eye piece, and remarked : — 



Dr. Beale in "How to work with the Microscope," has recom- 

 mended the use of the "Kellner eyepiece" as a condenser, and says 

 "by stopping off the greater part of the light passing through the 

 condenser by placing over the upper lens a thin plate with a very 

 small central hole, great advantage results in working with high 

 powers." In the condenser shown by Mr. Bicknell, the amount and 

 direction of the light is controlled by a revolving diaphragm placed 

 between the lenses, where the diaphragm is usually placed in an eye- 

 piece; there are three holes of different sizes for direct light, one hole 

 with a central stop for dark field illumination, which gives an admira- 

 ble effect with objectives under 30° ang. ap., and there are two oval 

 openings and an oblong opening, especially for use with binocular in- 

 struments. The oval openings are opposite each other and are in use 

 at the same time, giving two oblique pencils of light converging to a 

 point. 



This condenser was used with various objectives from a 1\ in. to a 

 l-50th of an inch, giving ample light for the latter with the highest 

 eyepieces. 



With this condenser and a 1-5 of only 100° angular aperture, I 

 had seen the same test object that had required a 1-10 or 1-12, of 

 150°, when used without it. 



October 18, 1871. 



Vice President Dr. Chas. T. Jackson in the chair. Fifty- 

 five members present. 



Prof. Louis Agassiz delivered the following eulogy on Dr. 

 J. E. Holbrook: — 



