LIQUID AIR AND LIQUID HYDROGEN. Dr. HAMPSON'S AIR-LIQUEFIER is now made to a standard pattern, 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. MACMILLAN & CO.'S NEW BOOKS. TWENTY-SIX GRADUATED EXERCISES IN GRAPHIC STATICS, some in Two Colours, and with Skeleton Data to practise upon, and including the Application to Roofs, Moving Locomotives, Retaining Walls, Lévy's Steel Arches, Girders (Original Constructions), Masonry Arches, Lévy's Weight Tables, with an Essay on Graphical Statics, in the form of a Running Commentary on the Exercises, each of which has full Instructions printed on its face, the whole forming a Supplement to the Authors' Elementary Applied Mechanics. By T. ALEXANDER, M.Inst.C.E.I., Professor of Engineering, Trinity College, Dublin; and THE PRINCIPLES OF ECONOMICS. A Fragment of a Treatise on the Industrial Mechanism of Society, and other Papers. By the late W. STANLEY JEVONS, LL.D., M.A., F.R.S. With a Preface by HENRY HIGGS. A MANUAL OF QUATERNIONS. By CHARLES JASPER JOLY, M.A., D.Sc., F.R.S., Sec. 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NOTICE.-Advertisements and business letters for NATURE should be addressed to the Publishers; Editorial Communications to the Editor. The telegraphic address of Nature is “ PHUSIS," LONDON. THE NEW HIGH POTENTIAL APPARATUS (GRISSON RESONANCE TYPE). Illustrated Descriptive Pamphlet now ready, post free. THE NEW GRISSON VALVE Illustrated Descriptive Pamphlet also now ready, post free. ISENTHAL & CO., 85 Mortimer Street, London, W. Printed by RICHARD CLAY AND SONS, LIMITED, at 7 & 8 Bread Street Hill, Queen Victoria Street, in the City of London, and published by MACMILLAN AND CO., LIMITED, at St. Martin's Street, London, W.C., and THE MACMILLAN COMPANY, 66 Fifth Avenue, New York.-THURSDAY, May 18 1905. be neatest, simplest, smallest and cheapest calculating machine ever designed. For adding up columns of figures rapidly and accurately. Can be used by anyone. "A necessity for all who have to add." Made entirely in steel and aluminium. Price 31/6 complete in leather case 6" x 33" x 1". NEWTON & CO., Scientific Instrument Makers to H.M. the King, H.R.H, the Prince of Wales, and the Government, See also page xxxiii in this issue. 3 FLEET STREET, LONDON. ISENTHAL & CO., 85 Mortimer St., London, W. PHOTOGRAPHIC LENSES. A SIMPLE TREATISE. 1/-, Post Free 1/3. This somewhat difficult subject is made clear without the use of mathematics. R. & J. BECK, Ltd., 68 CORNHILL, LONDON. PRACTICAL NOTES ON TELEPHOTOGRAPHY. Free on application to R. & J. BECK, Ltd., 68 CORNHILL, LONDON. |