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NATURE 



STANDARD LONDON 
PETROLOGIGAL Microscope 
Zz 
EA This instrument is supplied in two models, 
yy one having the analyser set over the nose- 
piece, the other having a complete analysing 
eyepiece. Both have all necessary adjust- 
ments, including double speed fine adjust- 
ment and centring rotating stage. The 
Becke lens fitting over the eyepiece is 
supplied for examining the rings and 
This instrument 
was fully described in 
come NatuRE of January 12, 
=: ) 1922. Price, with nosepiece 
analyser, eyepiece with 
crosswires, polarising 
and analysing prisms, 
in case, 
£23 17s. 6d. 
With eyepiece 
analyser with 
crosswires and 
polarising 
prism, in case, 
£24 1s. 















Complete descriptive Catalogue on application. 
R. & J. BECK, Lro., 68 Cornni, Lonnon, E.C.3. 







Limited, ‘ 
LABORATORY FURNISHERS. 
BALANCES AND WEIGHTS. 
Apparatus for Gas Analysis, Fat Extractions. 
Milk Analysis, Oil Testing, ete. 
Pure Chemicals and Standard Solutions. 
Dissection Instruments, Etc. 
76 DEANSGATE, 
MANCHESTER. 
Telegrams :—Pharmacy, Manchester. Telephone :—City 7942. 
Offices and Warehouse :—VICTORIA BRIDGE. 
Laboratories and Works :—KNOWLSLEY STREET. 

DARK GROUND ILLUMINATION. 
(For exhibition of Ultra Microscopic Particles, Spirochaete, etc.) 
Jas. WOOLLEY, SONS & Go., 
ly 
29 

BRITISH RESISTANCE GLASS 
Special Price List of Beakers, Flasks, etc.; on request, ; 
MICROSCOPES AND ACCESSORIES. 

WATSON & SONS have designed a highly efficient but very simple method of attaching an 
Immersion Paraboloid for Dark Ground Illumination, 
It is fitted immediately beneath the Paraboloid in a special carrier, with a suitable condensing lens. 
and one of the principal troubles in obtaining a good black background is obviated. 
For the former a resistance is required. 
the main current supply or a 6-volt dry battery. 
The above arrangement will be found invaluable in laboratory work. 
PRICES: 
Electric Lamp and Condensing Lens, as described above, with flexible wire . : y . £2 10 O 
6-volt Battery with switch, in box . 3 : : . : : : . : . 1m s 
Or for Main Current Supply—suitable Resistance for high voltages—100-125 volts 7 ‘ 1, the 
Do. do. do. 200-250 volts . A 2-20 
Watson's Immersion Paraboloid, completely mounted for Substage . ° . : . 410 0 
Do. do. for Understage . q : : F 5 315 0 
W. WATSON & SONS, 
ESTARLISHED 1837. 
LTD., 
electric lamp to their 
~ - 
It is therefore centred, — 
The fitting can be connected either to” 
Full particulars of the above will be sent post free on request. 
313 HIGH HOLBORN, 
LONDON, W.C.1 
WORKS: BELLS HILL, HIGH BARNET. 



Fitted with 5 draw tubes. In Nickel Silver throughout, highly 
polished. Length fully extended 15”, length closed 44”. Diameter 
of Object Glass 1”, magnification 20. Body covered in crocodile. 
PRICE £2:0: O post-free. 
Itlustrated Leaflets sent on request. 
Orion Works, Ealing, London, W.5. 

W. OTTWAY & Co. Ltd. 
(Established 1640) 
Actual Makers of Astronomical and Terrestrial Telescopes 
OTTWAY’S “SPOTTER” TELESCOPE 

Printed in Great Britain by R. & R. Clark, Lrp., Brandon Street, Edinburgh, an 
London, W.C.2, and Trt MacmiLtan Co., 66 Fifth Av 
» 3190 

Incorporating the HIGH TENSION COMPANY. 
DESIGNERS AND MANUFACTURERS OF 
TRANSFORMERS, y 
INDUCTION COILS, 
VACUUM TUBES, etc. 
11 Torrington Place, of. 
| Gower Street, London, W.C.1. 
Telephone: MUSEUM 8121 (3 lines). SEF 

ished by Macmittan & Co., Limitep, at St. Martin's Street, 
Jew York.—SaTuRDAY, June 30, 1923. 

