854 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



entirely new construction. They commence in both series with a 

 magnifying power of 4, and are convenient to work with even in the 

 highest numbers. The eye-point in all lies so high abovo the upper 

 surface of the eye-lens, and tbe diameter of the lens is so large, that 

 the usual inconveniences attending the use of eye-pieces of short focus 

 aro completely obviated. 



Tho ordinary drawing prisms, and particularly the Abbe camora, 

 may be used without difficulty on Nos. 4 to 18 inclusive. 



All the eye-pieces are supplied in cylindrical mounts, the external 

 diameter of which is 23 • 3 mm. for the Continental body, and 35 ■ mm. 

 for the English. Adapters to fit them to larger bodies can be made 

 by any workman. 



On each eye-piece is engraved the magnifying power, the focal 

 length and tube-length for which it is adapted, as well as the name of 

 the firm. 



Table of Magnifying Powers of the Apochromatic Objectives, with the 

 Compensating Eye-pieces for a Visual Distance of 250 mm. 



Projection Eye-pieces. — For such purposes as require the projec- 

 tion of a real image, but more particularly for overcoming the incon- 

 veniences which arise in photo-micrography when the objective 

 alone is employed, as also in the use of the ordinary eye-piece or 

 amplifier, a specially constructed projection series is supplied which 

 externally resemble eye-pieces, and fit into the body-tube of the 

 Microscope in the same manner. 



They consist of a convex lens and a compound system, which like 

 the apochromatic objectives, is most carefully corrected both spheri- 

 cally and chromatically, and is entirely free from any secondary 

 chromatic aberration, and free from difference of focus between the 

 visual and chemical rays. Between the convex lens and compound 

 system, a diaphragm is introduced for limiting the field. The 

 system can be made to approach or recede from the diaphragm. 



When used to project an image on a screen for demonstration, or 

 upon a photographic plate, the objective of the Microscope remains 

 exactly in the same condition as when observing with an eye-piece. 

 After a preliminary adjustment of the specimen by means of the 

 ordinary eye-piece, the projection eye-piece is put in its place and its 



