clvi NATURE [DECEMBER II, 1913. 
THE HERBERT SMITH 
“7 INEW.: AND , We. 2 Model) 
Pre le gives the refractive indices with- 
out. calculation to the second place of 
decimals, and by estimation to the third, 
and the instrument will accommodate any 
faceted stone, however large its size. 
IMPROVED «| 
MICROSCOPES 
SUITABLE FOR 
EVERY 
REQUIREMENT 
(from class work 
to the highest 
grade research) 
REFRACTIVE INDEX 
—== 1:30 
1:35 
1-40 
1-45 
150 
155 
1-60 
1-65 
in a variety of models, 
possessing many advan- 
tages over the older 
type, and embodying 
several important fea- 
tures not to be found 
in any others. 
The Herbert Smith Refractometer, in case complete 
with accessories and explanatory pamphlet rh . £660 
Pamphlet on the Refraectometer and its use, particularly for the 
: Discrimination of faceted Gem-Stones, which contains complete 
——— ILLESB RATED, tables of the physical characters of the Gem-Species and Index 
=— SH DESCRIPTIVE 
f to their varieties, also the Refractive Index of various liquids, 
Ee SECTIONAL by Dr. Herbert Smith, post free, 2/6 
= CATALOGUES : 
pe a J. H. STEWARD, Ltd. 
Opticians & Scientific Instrument Makers to the Brilish G Foreign Govts. 
18 BLOOMSBURY SQUARE, -W.C. 406 & 457 Strand, London. 
(A few doors from the British Museum.) ESTABLISHED 1852. 
PO a a a oo ee RNR SIE SS anes fins 
ABSORPTION-SPECTRUM OF RABBIT’S EYE. 
o NATORE, } Visible Invisible Spectrum 
November, Spectrum, 4 (Ultra-violet). 
1913. jt. ; 
x. The whole eye. 
2. Ditto, with ordinary 
white glass. y 
. Ditto, hard flint glass. 
(REGD.) 
The new Optical Glass for Spectacle Lenses actually absorbs 
the Ultra-violet or irritant rays, whilst the loss of visible light is 
only 5%. The selective action is due to the chemical constituents 
3 
of the glass which er from the usual coloured glass, 4. Ditto, with blue glass. 
in that its action does not depend upon colour: in fact, ‘SpECTROS’ . Ditto, with ‘Spectros’ 
is PRACTICALLY COLOURLESS. 5 ee ee 
Strongly recommended in all cases of eyestrain from bright light, 6. Ditto, with smoke 
for reading and sewing by artificial light, motoring, &c. glass. 
The new N‘O Tint does not differ in appearance from ordinary 
spectacle lenses. Write for illustrated explanatory Booklet. 
SUPPLIED ONLY BY— Prescribed by the leading Opthalmic Surgeons. . ~ 
W. WATSON & SONS, Ltd. (F**33!s"e?), 313 High Holborn, London, W.C. 
Optical Works—HIGH BARNET, HERTS. (2 EASY ROW, BIRMINGHAM. 
Branches {16 FORREST ROAD, EDINBURGH. Depots | 212 NOTRE DAME STREET, MONTREAL, CANADA. 
ran (184 GREAT PORTLAND STREET, LONDON, W. \78 SWANSTON STREET, MELBOURNE, AUSTRALIA. 
SPENCER MICROSCOPES 
Most Up-to-date Designs. 
Very Best Material and Workmanship. 
PRICE LIST ON APPLICATION. 
SOLE AGENTS FOR GREAT BRITAIN AND IRELAND (except London) — 
STANDLEY BELCHER & MASON, 
LTD., 
CHURCH STREET, BIRMINGHAM. 
ed 1 5 S is nD Co., LimiTED, at 
Printed by RicHarp Cay & Sons, Limirep, at Brunswick Street, Stamford Street, S.E., and published by MACMILLAN AND 2 4 
“St. Martin's Street, London, W.C., and THe MAcmILLAN Co., 66 Fifth Avenue, New York.—Tuurspay, December rr, 1913. 
C1LZ | REFRAGTOMETER 
