256 THE AMERICAN MONTHLY [Aug 



Oil Immersion Condenser. — Messrs. Watson and Sons 

 have sent out a new "Parachromatic Oil Immersion Con- 

 denser. For an objective to work at its best, the aperture 

 of the condenser should approximate to that of the objec- 

 tive. Though it is not every objective that will stand so 

 large a cone of light, the best of our immersion lenses need 

 a larger aperture of illumination than the 170 deg. or so, 

 that can nominally be passed through them with an ordin- 

 ary dry achromatic condenser. The total aperture of this 

 condenser is 1.35 N. A., and its aplanatic aperture is be- 

 tween 1.25 and 1.3 N. A. The clear apei ture of the back 

 lens is 6-10 inch, and the power of the condenser is equiv- 

 alent to an objective of % inch focus. It works through a 

 slip 1'75 millimeteres thick, and the makers state that to 

 get the best results the lamp should not be less than 5 

 inches, or more than 7 inches from the back of the lens. 

 With this condenser and a fine achromatic immersion ob- 

 jective of similar aperture, we have obtained results that 

 closely rival the apochromatics. It is an essential part of 

 the outfit of the student of bacteria, the diatomist and 

 others. The price is so moderate as to bring it within the 

 reach of most microscopists. The optical portion only, 

 with universal objective thread, costs $26 whilst the whole 

 mounted with iris diaphragm, graduated to show aperture 

 in use, stops, and revolving carrier is $31. 



Abbe Camera Lucida. — Messrs, Bausch and Lomb have 

 also brought out a simplified form of this camera, in which 

 the mirror and prism are enclosed in a mount and fixed, the 

 mirror itself being reduced in size. The whole is attach- 

 ed to ihe microscope by a clamp, and can be swung aside as 

 required ; whilst it can further be adjusted in position so 

 as to be used with various eye-pieces. 



New Stage Table. — It was first devised as a rough stage 

 for the microscope. That instrument being placed verti- 

 cally, the table is brought over its stage, and admits work 

 of the roughest character without danger to the micro- 

 scope. Further, it can be heated by aid of a spirit lamp, 

 12nd when hot enough placed over the microscope, thus act- 



