CXCVl 



NATURE 



{April 1"], 1879 



CEOOKES' 



ULTRA GASEOUS STATE OF 



MATTEE. 



MESSRS. MAWSON & SWAN 



Are prepared to supply the following Vacuum Tubes illustrating 

 Mr, Crook es' recent researches : — 



1. THE ELECTRICAL RADIOMETER, 



shewing the dark layer of freely vibrating molecules by which, on Mr. 

 Stoney s theory, the rotation is effected. 



2. THE CUP ELECTRICAL RADIOME- 



TER, shewing the convergence of the molecular streams on the concave 

 side of the vane. 



3. THE "BLUE FOCUS," a Concave Re- 



flector at moderate exhaustion, shewing the remarkable appearance of 

 a luminous focus in an " optically pure" vacuum, without the presence 

 of any solid or floating particles. 



4. THE "GREEN FOCUS." 



At this extreme exhaustion the momentum of the molecules is ex- 

 pended on the glass, which becomes fluorescent at the focus, and very 

 hot. ' 



5. MOLECULAR SHADOWS. 



The molecules impinging on the surface of the glass render it fluores- 

 cent, except where diverted by any solid object placed in their path. 

 Hence apparently black shadows of glass figures are projected on the 

 bulb, and if the molucules are caused to alter their path by bringing a 

 magnet near to the tube, the shadows are twisted out of their position. 



MAWSON & SWAN, NEWCASTLE-ON-TYNE. 



EUDOLPH KOENIG, 



(DR. PHIL.) 

 MANUFACTURER OF 



ACOUSTICAL INSTRUMENTS. 



TO ILLUSTRATE THE LAWS 

 AND TO PRODUCE THE PHENOMENA OF SOUND. 



PARIS, 26, RUE DE PONTOISE. 



PRICE LISTS FREE. 



MICROSCOPES, OBJECTIVES, &c. 



CENTENNIAL EXHIBITION, PHILADELPHIA, U.S.A. 



The Medal and Highest Award has been given for Design, 

 Construction, Optical Excellence, and Moderation in Price, to 



HENRY CROUCH, 



66, BARBICAN, LONDON, E.G. 



Fully Illustrated Catalogue and full Instructions by Post, 6 Stamps. 

 Mailed abroad free. 



0. TISLEY & Co. 



OPTICIANS, '' 

 17 2, BROMPTON ROAD, S.W. 



(Close to South Kensington Museum). 



THE PHONEIDOSCOPE 



An IiLStrument for Observing the Colour-Figures of Liquid Films under the 



action of Sonorous Vibrations. 



Being a visible demonstration of the Vibratory and Molecular Motion of a 



Telephone Plate. 



The PHONEIDOSCOPE, with 3 Discs, Bottle of Solution, Descriptive 



Pamphlet, &c., in Cardboard Box, xas. 6d. 



MANUFACTURED AND SOLD VITHOLKSALK AND RETAIL BY 



S. C. TI.SLEY & CO., 172, BROMPTON ROAD, LONDON, S.W. 

 TELEPHONIC ELECTRICITY. AU Materials suppUed for expeji- 

 mental purposes. 



Price Lists of Electrical and Aeottstic Apparatus, with Drawings and 

 Description of the Harmonos^raph, Post Free, zd. 



BARCLAY & SON, 



138, REGENT STREET, LONDON. 

 To Her Majesty and IT.R.H. the Prince 0/ Wales. 



DUPLEX LAMPS. 

 MODERATOR LAMPS. 



READING LAMPS. 



MICROSCOPE LAMPS. 



BEST COLZA OIL. 



A I KEROSINE OIL. 



WAX, SPERM, 



AND 



PARAFFINS CANDLES. 



ILLUSTRATED CATALOGUES POST FREE. 

 NOW READY, 



SECOND EDITION, 



GRIFFIN'S 



CHEMICAL HANDICRAFT. 



PRICE 4*. jd. POST FREE. 



A CATALOGUE OF CHEMICAL APPARATUS: 



ILLUSTRATED, CLASSIFIED DESCRIPTIVE. 



Demy 8vo, 480 pp.. Illustrated with 1,600 Woodcuts. 



Most Complete dnd Cheapest List of Apparatus. 



JOHN J. GRIFFIN and SONS, 22, GARRICK STREET 

 LONDON, W.C. 



EDWARD PATERSON, 



Electrical Engineer and Scientific Apparatus Manufacturer, 



3, BEDFORD COURT, COVENT GARDEN, LONDON. 



STEAM WORKS, GRAY'S INN ROAD. 



Experiments in Electric Lighting carried out. 



Electrtcal Apparatus of all descriptions for Lecture Purposes 



Loaned out. 



FOR CLASS 



DEMON- 



APPARATUS 



STRATION and for SCIENCE SCHOOLS. 



ELECTRIC LIGHT APPARATUS. 

 SIEMEN'S and GRAMME'S DYNAMO 



MACHINES and LAMPS for Hire and Purchase. 



LARGE ASSORTMENT of RUHMKORFF 



COILS and VACUUM TUBES. 



PROFESSOR HUGHES' MICROPHONE. 

 ELECTRIC BELLS and INDICATORS. 

 TELEPHONES and TELEPHONE CALL 



BELLS, WIRE, &c., for Fixing. 



PROF. S. P. THOMPSON'S LANTERN 



SLIDE GALVANOMETER, aof. 



EDISON'S ELECTRIC PEN £8 8s. 

 ELECTRIC and MAGNETIC APPA- 

 RATUS of all Descriptions. 



New niustrated Catalogue of (to pages post free 6 stamps. 

 Orders over £a carriage paid to any part of the United Kingdom. 



Printed by R. Clay, Sons, and Taylor, at 7 and 8, Bread Street Hill, Queen Victoria Street, in the City of London, and published by 

 M/CMUIAN A>D Co., at the Office, 29 and 30, Bedford Street. C( vent Garden.— Tnurf day. April 17, 1879. 



