December 29, 192 1] 



NATURE 



CXXXIX 



SLIDING 

 RESISTANCES 



in a VARIETY OF PATTERNS for 



ALL R EQUIREM ENTS. 



Quality up. Prices down. 



ISENTHAL & CO., LTD., 



Contractors to the Admiralty, War Office, India 

 Office, Colonial Office, Postmaster-General, &c. 



DENZIL WORKS, WILLESDEN, 

 LONDON, N.W. 10. 



WANTED, QUARTZ LENSES, CORNU 



PRISM, etc., suitable for making spectrograph. Or to buy or hire 

 complete spectrograph. London. 



Box 2722, c o N'ature Office. 



SCIENTIFIC APPLIANCES and materials 



for Electrical, Magnetic, Optical and Experimental work. 



New and Secondhand .Apparatus and parts by high-class makers. 



Lenses, Prisms, Mirrors. Static machines, Spark Coils, 



Relays, Wires, Cells and Accumulators. Kifty years' experience. 



Call and see stock, or write us. Our New Illustrated Catalogue 6d. 



post free. 



Seientiflc Appliances (Dale & Hollins), 11 & 29 Sicilian 



Avenue, London, W.C. 1. 



THE HANDBOOK OF 



PATENT LAW OF ALL COUNTRIES 



By W. P. THOMPSON, F.C5., M.I.Mech.E., Etc., 

 Chartered Patent Ag^cnt of Liverpool. 



Entirely revised and re-written 1920. 157 pages. Crown Octavo. 



All Countries, 6s. British Law only. Is. 

 " Should prove a very valuable and trustworthy guide to would-be 

 patentees. ' ' — Nature. 



London : Stevens and Sons, Limited. 



USE 



■ DUSTLESS ROOMS I 



On all Laboratory, Library, Museum, School, &c., 

 Floors and Linoleums of every description 



FLORIGENE 



(Regrd.) 

 DURING the VACATION for BEST RESULTS. 



It is IMPORTANT TO NOTE that ONE APPLICATION of 

 ••Florigene" ALLAYS the DUST and DIRT for 2 to U months. 

 according to traiBc, not only during each Sweeping (without 

 Sprinkling of any kind), but also throughout all the intervening 

 periods— which is of greater hygienic importance. Easily applied. . 



These sanitary and laboor-saving advantages are NOT 

 attained by sweeplng-poisders or any other method. 



Stnd fcr Particulars, MedicaL Reports, ani Ttstinionials to the 5i'.> Maktrs 



The "I>UST-Ar-i:.JL^5rEI«»» Co. 



4 VERNON PLACE, BLOOMSBURY, LONDON, W.C. 1. 



Contractors to Aa 



ally. H.M. Office o/U\ 



jouts., L.C.C., etc. 



