SCIENCE 



New Series. 

 Vol. IX. No. 223. 



Friday, April 7, 1899. 



Single Copies, 15 cts. 

 Annual Subscription, S5.00. 



WM. GAERTNER & GO. 



Astronomical and Physical Apparatus 



152-158 East 56th St., CHICAGO 



LEVEL TESTER. Price, $12.50 



SPECIALTIES 



Standard Apparatus of New and improved Designs 

 Astronomical Telescopes reading Microscopes and telescopes dividing Engines, Compara 



Spectroscopes Bolometers General Laboratory Appar 



MiCHELSON interferometers HeLIOSTATS U ?J IVE RSAL LABORATORY SUPP 



MINIATURE INCANDESCENT LAMPS. 

 MINIATURE LAMP RECEPTACLES. 

 X-RAY" TUBES AND APPARATUS. 

 FLUOROSCOPES ^ 



Catalogues on Application. 



EdisoD Decorative and Miniatare Lamp DeparliDent, 



(General Electric Company,) 



HARRISON. N. J. 



Q|]p.L|r||.Qrl Qlinllo ^ growing interest is manifested by Concliologists in the interior structure of 

 OcULIUIlCU Ollulldi univalve mollusks as revealed by sectioning. To supply their cabinets we are 

 ^"^~^~~"~^^^"^"''^^~~^^~~ furnishing shells cut on our steam diamond saws, in any desired direction, at 

 a small advance over our regular list prices. Cut Nautilus, Murex, Voluta, Strombus, Cyprjea, Cassis, 



Trochus, etc., etc., always in stock. Write for our circulars, naming your special field. 



"WARD'S NATURAL SCIENCE ESTABLISH BIENT, 



28 to 40 College Avenne. 



ROCHESTER, N. Y. 



WrQTHN VOLTMETERS 



¥f LO I Un AND AMMETERS 



are rec0g;nized throughout the civilized world as standard. 

 They cost more than other instruments, but results obtained 

 are proportionately more satisfactory. 



I am Special Agent for the ^Yeston Electrical Instrument 

 Co., and solicit correspondence with all readers of '' Sciknce" 

 who require the best apparatus for electrical measurements. 



Catalogue X (a complete price list of Weston Instruments) 

 mailed free upon request. 



JAMES G. BIDDLE 



1034 Drexel Bnildiug PHILADELPHIA 



