cxiiv 



NATURE 



[December 2q, 192 i 



BECK STANDARD LONDON 

 MICROSCOPE— MODEL L 



This instrument is a first-grade Micro- 

 scope, which can be supplied as a 

 simple microscope at a moderate price. 

 In its complete form it has a mechan- 

 ical stage, swing-out rack and 

 pinion and centring substage, and 

 all apparatus for ihe most exacting 

 bacteriological and biological work, 

 but the parts which 

 convert it from a simple 

 student's instrument into 

 a complete research 

 model can be purcha'-ed 

 separately and 

 attached to it by 

 the owner with- 

 out the necessity 

 of returning the 

 instrument to the 

 maker. 



Descriptive Booklet 

 sent on application. 



R.&J.BEGK.Ltd., 

 68 GORNHILL, 

 LONDON, E.G.3 



Messrs. NEWTON & Co., 72 Wigmore St., London, W.I, hold 

 a representative stock of Beck Microscopes and Apparatus. 



The STUDENT'S GONIOMETER 



Constructed to the design of Dr. G. F. Herbert Smith, of the 

 Mineral Department of the British Museum, and embodying 

 many improvements over existmg types. 



The Mirror is adjustable in any direction. The crystal holder 

 and attachments facilitate the measurements of the crystal without 

 readjustment, and a removable pointer is provided to ensure the 

 adjustment into the axial line. The graduated circle of 5 inches 

 (i2'5 cm.) in diameter is fitted with a clamp and fine adjustment, 

 and the Silvered Scale is divided to half degrees, reading by 

 vernier to minutes of arc. Price - £9 10 



J. H. STEWARD, Ltd. 



opticians and Scientific htstrument Makers to the British and 

 Foreign Governments 



406 and 457 Strand, London, W.C.2. 



Established 1852. 



NEW OBJECTIVES 



WATSON'S 1 7-In. OIL IMMERSION LENS. 



Only those who have used a low power Oil Immersion Objective can form a conception of the superlative effect 

 which is obtained with it. The ease of manipulation, the brilliance of illumination,, and the wonderful definition 

 combined in WATSON'S new 1/7" OIL IMMERSION LENS, render it what it is designed to be, viz., a substitute for 

 the 1/6" Dry and 1/12" Oil Immersion Objectives. 



A large amount of the work done with the 1/12" is with dark ground illumination, for which the numerical 

 aperture has to be cut down by means of a funnel stop. The new 1/7" is made with a numerical aperture of -qo. It 

 requires no cutting down, and can be used for the examination of spirochaetse or for ordinary biological specimens. 



It is the latest. It is the best. It is cheap — Price £5 . 15 . 



Full particulars of the above and other Objectives are contained in Watson's Catalogue of Microscopes, 



post free on request. 



W. WATSON & SONS, Ltd., 313 High Holbom, London, W.C.I 



ESTABLISHED 1837. 



WORKS : HIGH BARNET, HERTS. 



A few of the many advantageous features of 



SPENCER MICROSCOPES 



Automatically lubricated fine adjustment bearings. 



Black lacquered body tubes, avoiding reflection of light into eyes of user. 



Low compact construction (considerably lower than others), which affords greater 



ease and comfort in using. 

 Low position of the fine adjustment, head away from the mouth and breath of the user. 

 Extra large stages with unusual distance from optical axis to base of the arm. 



Spencer Microscopes represent careful attention to 

 the little things which generally escape attention. 



STANDLEY BELCHER & MASON, Ltd., Church Street, BIRMINGHAM 



Printed in Gr at Britain by The Coknwalu Press, Ltd., Paris Garden, btainford Street, S.K.i, and pu lishe I by AIac.milla.n and Co., Limited, 

 at St. Martin's Street, London, \V.C2, and The Macmillan Co., 66 Fifth Avenue, New York. — Thursday. December 29 1921. 



