ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



487 



(2) Eye-pieces and Objectives. 



Zeiss' Objectives.* — The Zeiss firm guarantee that their achromats 

 ami apochroiuats may now be classed among durable objectives, and 

 may, without hesitation, be used even under such unfavourable climatic 

 conditions as obtain in maritime and tropical districts. 



In the achromats E and F the guaranteed minimum value of the 

 numerical aperture has been raised from - 85 to 0*90, and in the case 

 of the T V~im homogeneous-immersion from 1 * 25 to 1 * 30. 



Demonstration Eye-piece.f — L. Murbach thinks that the well- 

 known difficulty of leading a pupil to identify objects (especially when 

 moving) under the Microscope may be got over by some kind of demon- 

 stration eye-piece, whereby both teacher and pupil may view the object 

 at the same time. The principle of his idea is shown in fig. 99. The 



;~? 



33 



Fig. 99. 



device consists of an ordinary eye-piece with cross-hairs for pointing 

 out the object. A prism above the eye-piece is so placed as to reflect 

 the image through a tube at right angles to the eye-piece to another 

 prism at the end of the tube. This prism will reflect the image upward 

 into the eye. 



Oculars for General Laboratory Work.J — J. H. Schaffher says that 

 Microscopes intended for general laboratory work, as for example, the 

 Bausch and Lomb BB4, are usually fitted with the 2-inch and 1-inch 

 eye-pieces ; but he recommends that the inch should be replaced by a 

 |-inch, the 2-inch being retained. 



Pulfeich, C. — TJeber neuere Anwendungen der Stereoskopie und iiber einen 

 hierfiir bestimmten Stereo-Komparator. 



[Discusses, inter alia, the principles of the Microscope-Stereoscope.] 



Ze.it. f. Imtrumenkunde, XXII. (1902) pp. (35-81 (4 figs.). 

 Stkehl, K. — TJeber die Gauss-Bedingung bei Mikroskopobjektiven. 



[Explains the principles on which apochroniatic lenses are made, and how 

 the conditions for colour-correction are determined.] 



Central-Zeit. /. Opt. u. Mech., XXIII. (1902) pp. 76-7. 



* Zeiss' Catalogue, 1902, and special circular, 

 t Journ. App. Mior., v. (1902) p. 1648 (1 fig.). % Tom. cit., p. 1646. 



