IMPORTANT ANNOUNCEMENT. D'Arsonval's Latest (1904) Apparatus, DISPENSING WITH COILS & INTERRUPTERS. For producing, perfectly regulating, and exactly measuring X-RAYS & HIGH-FREQUENCY CURRENTS. (Protected by Numerous Patents.) SILENT IN WORKING. SIMPLE IN MANIPULATION. This apparatus has been already installed by many of the chief workers in Electro-Therapeutics in France and England where the apparatus may be seen working. WATSON'S MICROSCOPES & OBJECTS. Watson's New Club" Microscope. An Instrument of full size of most modern design. Especially arranged for the use of Amateurs. Monocular, £15; Binocular, £18. Watson's well-known Van Heurck and Edinburgh Student's Micro- The Watson-Conrady Condenser System is of new computation, and for the Microscopist. Everything New Slide of Radium for Microscope. Shows Scintillations Trypanosoma Brucef (Sleeping Sickness) each ... Exquisite arranged groups composed of Diatoms, Spicules, &c., Write for Catalogue No. 3 of Micro. Objects, together with newly For all the above see WATSON'S 158-page Catalogue of Microscopes, sent published supplementary list of Slides, giving details of recently post free. added specimens, post free. SPINTHARISCOPE for observing the Scintillations of Radium. The very best. Price 21/SPECIALITIES:-STRUTT'S RADIUM CLOCK. Price according to quantity and quality of Radium included. RADIUM of MAXIMUM activity in stock, also of medium and moderate activities. Send for particulars. W. WATSON & SONS, 313 HIGH HOLBORN, LONDON, W.C. ESTABLISHED 1837. COUNTRY BRANCH-16 Forrest Road, Edinburgh. GAS PLANT. GAS ENGINE AND DYNAMO. Electric Current for 100 16-c.p. lamps can be obtained for ONE PENNYWORTH of fuel per hour by using a CROSSLEY An excellent lens for all artistic photography. THE ADON (REGISTERED) Dallow yer LONDON ADON CASTING PATENT. Mounted in Aluminium. Measures 3ins. long, 1 ins diameter, weighs 4 ounces. PRICE, including Solid Leath:: Case, £3 10 0 nett. ILLUSTRATED BOOKLET with Specimens of Work FREE. J. H. DALLMEYER, LTD., 25 Newman St., London, W. Printed by RICHARD CLAY AND SONS, LIMITED, at 7 & 8 Kread Street Hill. Queen Victoria Street, in the City o London, and published by MA AND CO., LIMITED, at St. Martin's Street, London, W.C., and THE MACMILLAN COMPANY, 66 Fifth Avenue, New York.-1HURSDAY, Feb The Gas Committee of the City of Birmingham require the services of a thoroughly trained CHEMIST, qualified to take charge of a new 20 ton per diem coal testing plant fitted with regenerative retort settings. Appli. cants must be capable of undertaking the following duties:-The analysis of coal and the by-products of coal, the analysis of furnace gases and the regulating of the gas plant, the manufacture of gas, including purification, analysis and test for illuminating power and of calorific value, the testing of all materials used in manufacture, and also the initiation and conduct of experiment and research work to aid the scientific development of the industry. Applicants are required to furnish particulars of their scholastic attainments in chemistry, state their age and experience, and salary required, and forward their application, addressed to the CHAIRMAN of the Works Sub-Committee of the Gas Department, Council House, Birmingham, on or before February 20 next. G. HAMPTON BARBER, Secretary Council House, Birmingham, January, 1905. CITY AND GUILDS CENTRAL TECHNICAL COLLEGE, EXHIBITION ROAD. CIVIL AND MECHANICAL ENGINEERING DEPARTMENT An ASSISTANT is required who can teach Mechanical Drawing and Mechanism;- applicants should have had some experience in the Drawing Office of a Mechanical Engineering Firm. Apply, sending testimoniais with a statement of age and particulars of teaching experience, to Prot W. E. DALBY. Salary, £150 per annum. MATHEMATICAL DEPARTMENT. An ASSISTANT is required immediately who possesses a sound know ledge of Elementary Mathematics and of the Elements of the Differenti.. and Integral Calculus. Some experience in a Mechanical or a Physic..' Laboratory and some knowledge of Geometrical Drawing is desirable, but not necessary. Salary, 100 per annum. Apply, sending testimonials and a statement of age, to Prof. O. HENRICI. The post of PROFESSOR of PATHOLOGY and BACTERIOLOGY at the School of Medicine, Cairo, is vacant. Pay, £800 per annum, privat practice not allowed. Applicants should forward copies of testimonials and Such other documents as are mentioned in the printed particulars respecting the post, which may be obtained from the Secretary of the Conjoint Board of England, Examination Hall, Victoria Embankmeat, London. The latest nail by which applications may be posted will leave London Du Friday, February 17. Applications to be addressed to the DiSECTOR, Government School of Medicine, Cairo, Egypt. COUNTY BOROUGH OF BELFAST. BELFAST PUBLIC LIBRARY. The Committee are prepared to receive applications for the post of CURATOR of the Art Gallery and Museum from competent persons, at a salary commencing at £150 per annum, age not to exceed 40. The gentleman appointed will be required to give his entire time to his official duties. Apply, stating experience, and enclosing copies of testimonials, to be sent to the undersigned on or before Wednesday, February 22, 1905. SAMUEL BLACK, Tewn Clerk. (Registered in Column B (Advanced Education). Teachers Registration Chemist, with good academic qualifications, Council, Board of Education, S.W.), 49 and 51 IMPERIAL BUILDINGS, LUDGATE CIRCUS, E.C. seeks appointment. Experience: Electrolytic, Metallurgical, Orgatis and Mineral Analysis and Research. N. D. L., ‹ð NATURE. UNIVERSITY OF LONDON. GOLDSMITHS COLLEGE, NEW CROSS. The following appointments will shortly be made in the department for the Training of Teachers, which will be opened on September 28, 1905 :(a) A VICE-PRINCIPAL and MASTER OF METHOD. (6) A VICE-PRINCIPAL and MISTRESS OF METHOD. The salary attached to each post will be £500 per annum, without residence. Applications must be received not later than March 6. Further particulars may be obtained from the PRINCIPAL, University of London, South Kensington, S. W. ARTHUR W. RÜCKER, Principal. MARLBOROUGH GRAMMAR SCHOOL. APPLICATIONS are invited for the position of HEAD MASTER of this school. Commencing salary, £250. Candidates must not be more than 35 years of age, and must be Graduates of some University in the United Kingdom. Full particulars, together with a form of application, will be supplied by the undersigned. Application must be made before April 1. Work commences in September. H. G. CANE, Acting Clerk to the Governors. 7 High Street, Marlborough. WANDSWORTH TECHNICAL INSTITUTE. SECONDARY DAY SCHOOL. An ASSISTANT MASTER required for French (modern conversational methods) and some general form work. Commencing salary, L120 to £150, according to qualifications and experience. Applications to be made before February 20 on forms supplied by the REGISTRAR, from whom further particulars can be obtained. TO SCIENCE AND MATHEMATICAL MASTERS.-Easter (1905) Vacancies.-Graduates and other well qualified Masters seeking posts in Public and other Schools for next term should apply at once, giving full details as to qualifications, &c., to Messrs. GRIFFITHS, SMITH, POWELL & SMITH, Tutorial Agents (Estd. 1833), 34 Bedford Street, Strand, London. Immediate notice of all the best vacancies will be sent. Manager of Scientific Instrument Factory Wanted. Workshop and electrical experience indispensable. Progressive salary. Give all particulars. Endorse "Private."-REYNOLDS AND BRANSON, LTD., Leeds. For Sale.-Extensive Collections of British Lepidoptera, Coleoptera, Tropical Butterflies, Cabinets, &c. Correctly named type collections at very moderate prices.-Particulars from A. FORD, Hillside, Sunnyhill, Pokesdown, Bournemouth. GLEW'S GLEW'S SCINTILLOSCOPE PATENT SCREEN PITCHBLENDE SCINTILLOSCOPE (PATENT). Shows a magnificent display of scintillations, howers 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 Pitch blende mineral, ground flat and polished, with Sensitive Screen attached, for use in Scintilloscope or with any strong pocket magnifier, from 75. 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. JUST OUT. The FEBRUARY issue of our List of SECOND-HAND INSTRUMENTS, Consisting of 25 pages of articles, by the best makers, in the VARIOUS BRANCHES OF SCIENCE. Post Free to readers of NATURE. C. BAKER, 244 HIGH HOLBORN, LONDON, W.C. SCHOOL BOTANY. We have prepared for use in Primary and Secondary Schools Collections of Specimens of Various Woods. They are very carefully selected in cross and long sections, in order to show the distinctive features and marks of each individual wood, and also to show their well-marked Botanical Characteristics, such as the Bark, Rings of Growth, Medullary Rays, &c., &c. We are convinced they will be of great practical use to the teacher. They cover a wide range of British and Foreign Woods, comprising all those usually met with. In Boxes, containing 20 large Specimens, 48. 6d. We would also call your attention to a Specially Prepared Porous Paper for Drying and Preserving Botanical Specimens. It is far superior to ordinary Blotting Paper, in that it is much more porous, and at the same time, is freed from any substances likely to injure the delicate colour of the plants. It has the advantage of being cheaper also than the common Blotting Paper. Prices on Application. A. GALLENKAMP & Co., Ltd., 19 & 21 SUN STREET, FINSBURY, LONDON, E.C. NOW READY. In medium 8vo. With numerous Illustrations. CONSTRUCTIONAL STEELWORK: THIRD EDITION. Thoroughly Revised. Fully Illustrated. 30s. A PRACTICAL TREATISE ON BRIDGE-CONSTRUCTION: BEING A TEXT-BOOK ON THE CONSTRUCTION OF BRIDGES IN IRON AND STEEL. By T. CLAXTON FIDLER, M. Inst.C.E. "The instruction imparted is SOUND, SIMPLE and FULL."-Engineer. TWENTY-SECOND EDITION. With numerous Illustrations. 16s. A MANUAL OF CIVIL ENGINEERING. Comprising Engineering Surveys, Earthwork, Foundations, Masonry, Carpentry, Metal Work, Roads, Railways, Canals, Rivers, Waterworks, Harbours, &c. By W. J. MACQUORN RANKINE, LL.D., F.R.S. Pocket Size, Leather Limp, with Illustrations. Pp. I.-XII. + 834. Price 18s. net. (THE NEW NYSTROM.") THE MECHANICAL ENGINEER'S REFERENCE BOOK. A Handbook of Tables, Formulas and Methods for Engineers, By HENRY HARRISON SUPLEE, B.Sc., M.E. "The work should prove exceedingly useful not only to Students, but to Practical Engineers as well."-Railways. LONDON: C. GRIFFIN & CO., LTD., EXETER ST., STRAND. Mr. Edward Arnold's New Books. THE EVOLUTION THEORY. By AUGUST WEISMANN, Professor of Zoology in the University of Freiburg. Translated by Professor J. ARTHUR THOMSON and MARGARET THOMSON. Two volumes, Royal 8vo. With many Illustrations. 32s. net. ASTRONOMICAL DISCOVERY By HERBERT HALL TURNER, D.Sc., F.R.S., THE CHEMICAL SYNTHESIS Professor of Chemistry in the City and Guilds of London Technical College, THE BECQUEREL RAYS PROPERTIES OF RADIUM. By the Hon. R. J. STRUTT, Fellow of Trinity College, Cambridge. Demy 8vo. 8s. 6d. net. 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