NEW ILLUSTRATED LIST

No. 2 (90 PAGES) OF

ELECTRIC HEATING
APPARATUS

including several new forms for LABORATORY PURPOSES.

POST FREE ON APPLICATION.

NATURE says:-". . . add to the comfort and cleanliness of many operations in laboratories as well as in houses. The adaptability of the electric current, and the efficiency of the various forms of apparatus described in Messrs. Isenthal's catalogue, should encourage the use of electric energy as a source of heat." (See issue of September 22, 1904, page 511.)

PURE BROMIDE OF RADIUM

OF HIGH ACTIVITY.

Radium of the maximum activity, Wireless Telegraphy and other apparatus may be had on hire for Conversaziones, &c.

ISENTHAL & CO., 85 MORTIMER STREET, LONDON, W. Contractors to the Admiralty, War, India, and Colonial Offices, &c.

DR. HALDANE'S APPARATUS

FOR ESTIMATING

TOWNSON & MERCER.

ESTABLISHED 1798 (OVER A CENTURY).

RETAIL-89 BISHOPSCATE STREET WITHIN, E.C. WHOLESALE-34 CAMOMILE STREET. E.C. Scientific Apparatus Manufacturers and Laboratory Outfitters to the Home and Colonial Departments of H.M. Government, Scientific Institutions, Colleges, and the various Industries throughout the World.

THE

WANNER PYROMETER

FOR

MEASURING TEMPERATURES

FROM

900° C. to 2000 C. or 4000 C. Special advantages of this Pyrometer:

Exact determination of temperature.
Rapidity in reading off (within 2 to
3 secs.).

Can be used by any intelligent workman.
One instrument suffices for several furnaces.

May be obtained from

TOWNSON & MERCER, 34 CAMOMILE STREET, E.C.

THE STEREOSCOPIC COMPANY'S

This is a small portable apparatus designed by Dr. J. S. HALDANE, F.R.S., for the use of Medical Officers of Health, &c. A sample of air can, by means of this apparatus, be tested on the spot, the whole operation being quite simple.

SOLE MAKERS

See Commendatory Notice in "NATURE," August 13th, 1903, page 347.

C. E. MÜLLER, ORME & CO., Ltd., 148 High Holborn, London, W.C.

The Ideal Camera for BIRD PHOTOGRAPHY, NATURAL HISTORY SUBJECTS, PORTRAIT AND FIGURE STUDIES, ARCHITECTURAL & GENERAL WORK. Write for full particulars from ...

THE LONDON STEREOSCOPIC COMPANY, 106 & 108 REGENT ST., W., or 54 CHEAPSIDE, E.C.

ESTABLISHED OVER 60 YEARS.

Shows a magnificent display of scintillations, showers of sparks, direct from the mineral Pitchblende, Radium, Polonium, Uranium, Thorium, or any radio-active substance, even a Welsbach mantle contains sufficient Thorium to excite the very sensitive screen of the Scintilloscope, which is far more sensitive than the Spinthariscope. The Scintilloscope rivals the most delicate Electroscope as a detector of Alpha rays.

The eye sees an inexhaustible shower of stars of white light, giving a very realistic idea of the ceaseless activity of these marvellous substances which are producing the terrific bombardment causing this beautiful display.

See NATURE, September 29, page 535. Glew's Scintilloscope Superior Lens, with Extra-sensitive Pitchblende and Polonium Screens, giving brilliant effects, Complete, 7s. 6d., Post free, U.K. Foreign Postage extra, weight 2 ounces.

Pieces of Pitchblende mineral, ground flat and polished, with Sensitive Screen attached, for use in Scintilloscope or with any strong pocket magnifier, from 7s. 6d. each, according to size.

Radio-active supplies of every description, on Sale or Hire. Radium Bromide, 1,800,000 units on hire for lectures.

F. HARRISON GLEW, Radiographer (Silver Medallist, Paris, 1900),

156 Clapham Road, London, S.W.

RECTIFIED SPIRIT

(SPIRITS OF WINE).

ELECTRIC FLASHES, OR THE SYSTEMS OF WIRELESS TELEGRAPHY AND TELEPHONY.

By A. T. M. JOHNSON, A.M.M.C.I.E. Inventor of the Johnson-Guyott Systems of Wireless Secret Telegraphy and Telephony.

With an Introduction by Dr. RICHARDSON.
Cloth, 2s. 6d. net. Postage 3d.

"Is a very handy small octavo volume which contains a considerable amount of indexed information, which is rendered the more intelligible by numerous diagrams."-Liverpool Courier.

R. A. EVERETT & CO., Ltd., 42 Essex Street, LONDON, W.C. TO BOOKBUYERS AND LIBRARIANS OF FREE LIBRARIES.

The November Catalogue of valuable Second Hand Works and New Remainders, offered at prices greatly reduced, is now ready, and will be sent post free upon application to

W. H. SMITH & SON, Library Department, 186 Strand, London, W.C. DEPARTMENT OF TECHNOLOGY.

CITY

AND GUILDS OF LONDON INSTITUTE.-REPORT of the WORK of the DEPARTMENT for the SESSION 1903-1904, with Appendices containing Tables of Results, Lists of Drapers' Company's Textile Scholars and Exhibitioners, of Prize Winners and of Certificated Manual Training and Domestic Economy Teachers, with Extracts from Examiners' Reports, and Question Papers with Practical Exercises set at the recent Examinations. Now Ready, price 9d. net, postage extra. To be obtained from any Bookseller, or from the Publisher, Mr. JOHN MURRAY, Albemarle Street, London, W.

FOREIGN SCIENTIFIC BOOKS

and Periodicals promptly supplied at lowest rates.

CATALOGUES POST FREE ON APPLICATION.

W. MULLER,

METHYLATED SPIRIT

Special Quotations to large
Institutions.

BOORD & SON,

DISTILLERS SINCE 1750,
115-121 Tooley Street,
LONDON, S.E.

LIQUID AIR AND LIQUID HYDROGEN.

Dr. HAMPSON'S AIR-LIQUEFIER is now made to a standard pat: tern, and numbers are in use in University Laboratories and elsewhere in various countries. The whole apparatus is neat and compact and its parts very easily moved; the Liquefier, without stand, being a cylinder 17 inches high and 8 inches in diameter.

It begins to liquefy air in from 6 to 10 minutes after the admission of air at from 150 to 200 atmospheres pressure, making over a litre of liquid per hour.

It requires no auxiliary refrigerant and produces a perfectly clear liquid which requires no filtering.

The operator has only one gauge to watch and one valve to control. HYDROGEN LIQUEFIER to the designs of Dr. MORRIS W. TRAVERS for use in conjunction with Air-Liquefier.

For Prices and Particulars apply to the Sole Makers :BRIN'S OXYGEN COMPANY, LIMITED, ELVERTON STREET, WESTMINSTER, S.W.

With 30 Original Illustrations. Price 2s. 6d.
The HYGIENE of the MOUTH.

A Guide to the Prevention and Control of Dental Diseases.
By R. DENISON PEDLEY, L.D.S. Eng., F.R.C.S. Ed.,
Dental Surgeon to the Evelina Hospital, Southwark.

NOW READY.

SCHOOL:

A Monthly Record of Educational Thought and Progress.

Edited by LAURIE MAGNUS, M.A.
No. II. Price 6d. nett.

CONTENTS:

PRACTICE AND PRECEPT:

The Welsh Convention-Its Manifesto-And the Board-Education
Committees-Physical Training-Sir Henry Craik-Dr. Walmsley on
Engineering-Biology and Morals-Education in the Reviews.

REPORT OF THE DEPARTMENT OF TECHNOLOGY.
FURTHER REFLECTIONS ON EDUCATION. By Rt. Hon. R. B.
HAI DANE, M.P., &c.

ILLUSTRATION IN TEACHING. By Prof. JOHN ADAMS.
COMMON ROOM PAPERS. On Character-forming and the

Unclubbable Boy. By THEODORE WALKOND.

OUR LEADERS.-XI. Alexander Bain. (With Portrait.)
PHYSICAL DETERIORATION. By T. W. BERRY, Director of Edu
cation, Withington.
PHYSICAL EXERCISES IN DAY SCHOOLS FOR GIRLS. By

SUSAN CUNNINGTON.

.

Mr. HARTOG has edited this book to meet the requirements of candidates for the London Intermediate B.Sc. and B.Sc., for which the University of London now requires a knowledge of scientific French.

RIVINGTONS, 34 King Street, Covent Garden, London.

ARCON, HELIUM.

We have now in stock a number of Vacuum Tubes of the above Gases,

GUARANTEED PURE.

(THE SCIENTIFIC ROLL.)

No. 13 (32 pp., January, 1905) of an important work on this subject will contain matter relating to the constancy, variation and value of characters in bacteria which will interest all biologists. It will be posted free to any applicant whose address is sent before the end of 1904, but if sent later the charges will be Id. for the week ending January 7, 1905; 2d., January 14; 3d., January 21; 4d., January 28; 5d., February 4; 6d., February 11; Is. for later dates. The post mark will be taken as the time of sending, or, failing this, it will be inferred from

75a Camden Road, London, N.W.

Telegraphic Address, "Sphericity, London."

ILLUSTRATED PRICE LIST OF SPECTROSCOPES, &c., POST FREE ON APPLICATION.

ment may be made by unused stamps of any nationality.

Apply to A. RAMSAY,

4 COWPER ROAD, ACTON, LONDON, W.