ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 237 



-correction for actinic rays is surprisingly good, so that exquisite defi- 

 nition is obtainable, even with a projection ocular No. 4. Notwith- 

 standing the extremely wide aperture, the field is perfectly flat, so that 

 perfect photographic definition is obtained at the edges of a large circle 

 on the focussing screen. The lens can take an unusual quantity of 

 light, and the condenser and diaphragm can be opened at least 40 p.c. 

 more than with other lenses, and excellent photographic results still bo 

 obtained. 



Magnifiers.* — J. Dearness, of London, Canada, finds that many 

 students are incapable of getting the best results out of the simple 

 Microscope. Instead of a folding lens or tripod he uses, in his classes, 

 a watchmaker's glass with two lenses. The lens on the tip may be 

 removed, thereby rendering the remaining lens lighter to hold in the 

 eye, while at the same time giving sufficient amplification for most work. 

 The great advantage of this magnifier is that both hands are free ; but 

 the objection is that many students are unable to retain the magnifier 

 by the eyebrow. He has therefore had a detachable heavy watch-spring 

 added to the mounting. This spring goes round the head and, when 

 properly adjusted, holds the lens comfortably in a suitable position. 

 Even those who can use the lens in the ordinary way, find the necessary 

 fatigue minimised by this device. As the spring is detachable the glass 

 can be carried in the pocket, and used for simple hand magnification if 

 desired. 



Henocque. — Oculaire spectroscopique destine aux etudes de micro-speotroscopie. 



Compteg Rend. Soc. de Biol, L1I. (1901) No. 37, p. 1009. 



(3) Illuminating 1 and other Apparatus. 



Lens for Dark-Ground Illumination. — Messrs. Koss have added to 

 their list a new simple lens for dark-ground illumination. It consists 

 of a meniscus lens bored through the centre to receive a spot turned 

 out of vulcanite, and having a stem to drop into the hole in the centre 

 of the lens. A most perfect dark ground with the object brilliantly 

 illuminated is obtained. It can be fitted to any Microscope. 



Albrecht s Objective-Carriers.f — This piece of auxiliary apparatus 

 is adapted for receiving any desired number of objectives, which it sets 

 rapidly and accurately in their proper optical positions ; it also effects 

 any easy interchange among the objectives, and securely protects them 

 from dust. Fig. 44 gives a section, and fig. 45 a plan seen from above. 

 The apparatus consists essentially of a broad ring a, in reality, the cir- 

 cular section of a hollow cone, and by means of a collar b, with bayonet 

 clutch c, it is fastened under the tube d, and can be easily removed. 

 This ring a is immovable, and is provided under d with an opening 

 which forms a continuation of the tube. An arm f of the collar b sup- 

 ports the ring at its centre. On its under side a possesses a concentric 

 dovetailed groove which a ring g engages pushwise ; this ring is on its 

 inner side also provided with a dove-tailed tenon. The hollow part of 

 the ring a is provided, at the proper place, for receiving an objective 



■ Journ. App. Micr., 1901, pp. 1448-9. 



f Central-Zeit. f. Opt. u. Mech., xxiii. (1902) p. 2 (2 figa.). 



