ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 819 



again (for some minds) the ground formerly won and now so incon- 

 siderately put in peril of being lost. 



Harchek, a. — Optometer und Apparat zum Messen der Brennweiten und zum 

 Centriren optischer Linsen, System Nortli Harchek. (Optometer and apparatus for 

 measuring the foci of and centering optical lenses, — North Harchek's system.) 



Breslauer Aertztl. Zeitschr., XII. (18S8) p. 139. 

 Highest Magnifying Power. 



[Another specimen of the general ignorance on this subject. "What is the 

 highest magnifying power that has been obtained? In lS6i an eminent 

 microscopist expressed his opinion that in object-glasses with one twenty-fifth 

 of an inch focus the Microscope had reached its utmost attainable limit of 

 perfection. He added that it appeared impossible to separate or define lines 

 more numerous than 90,000 in an inch on account of the decomposition of 

 light. Yet witliin a few years after this opinion had been expressed, an 

 object-glass with a one-fiftieth of an inch focus was made which magnified 

 1,575,000,000 times. This revealed the one four Imndred thousandth part of 

 an inch ; but it again has been left far behind by a glass recently made in 

 Sweden, which enables us to distinguish the one two hundred and four 

 million seven hundred thousandth part of an inch."] 



Tit-Bits, XIV. (1888) p. 310. 



Meegiee, G. E. — Traite pratique de Manipulations de Physique a I'usage des 



Etudiants en Medecine, precede d'une Preface par M. le Prof. C. M. Gariel. 



Optique. (Practical treatise on physical manipulations for students in medicine. 



With a preface by Prof. 0. M. Gariel. Optics.) 



iv. and 251 pp. and 90 figs., Svo, Paris, 1888. 

 Nelson, E. M. — On the Interpretation of a Photomicrographic Phenomenon by the 

 Abbe Diffraction Theory. Joum. Qiiek. Micr. Club, III. (1888) pp. 273-9. 



„ „ True and False Images in Microscopy. 



Joum. Quek. Micr. Club, III. (1888) p. 288. 

 „ „ Amphipleura pellucida. 



[Keport of resolution with Powell's 1/4 in. objective 1-17 N.A. with dry 

 froat, i. e. with I • N.A.] Eiigl. Mech., XLIII. (1888) p. 51. 



Smith, T. F. — On True versus False Images in Microscopy. 



Joum. Quek. Micr. Club, III. (1888) pp. 267-72, 288-9. 

 Tanakadate, a. — Note on the Constants of a Lens. 



Joum. Coll. of Sci. Tokio, I. (1888) p. 333. 

 V E E E K E E, J. G. P. — Numerical Aperture. 



Joum. of Micr., I. (1888) pp. 155-66 (4 figs.). 



(6) Miscellaneous. 



Simple method of Projecting upon the screen Microscopic E.ock 

 Sections, both by ordinary and by polarized light.* — Mr. E. P. 

 Quinn " knowing the difficulty experienced in pointing out to students 

 any particular crystal in a rock section when viewed with the Microscope 

 direct, attempted to project the images on the screen, and by the aid of 

 comparatively simple apparatus met with very gratifying success, both 

 with ordinary and with polarized light. 



The tube of the Microscope was screwed out and replaced with a 

 cork, through which a hole had been cut to carry the ordinary 1 in. 

 objective, and behind it the analyser of the Microscope. The polariscope 

 and rock section occupied their usual position as when used with the 

 Microscope in the ordinary way. The Microscope-stand being inclined 

 into the horizontal position was placed in front of the object-lens of the 

 limelight lantern. The object-lens of a lantern usually consists of a 

 combination of two lenses. If so the back lens is taken out and the front 

 lens only used, acting as an extra condenser, concentrating the light 

 upon the rock section and causing it to pass through the polarizer and 

 the analyser. 



* Eep. Brit. Assoc. Adv. Sci., 1887, p. 725. 



