SCIENCE— ADVERTISEMENTS 



cA Sign of Quality ^^^1SIq| ^ Mark of Service 



f "^ ^i^^^ft.^ 



Ask for the 12-page Hand- 

 book of instructions for 

 demonstrating all the funda- 

 mental laws of optics by use 

 of an optical disc. Nearly 60 

 illustrations. 



3675. OPTICAL DISC enabling the demonstration 

 of all the fundamental laws of optics, in connection with 

 any text. Visible to the entire class, showing the prin- 

 ciples of refraction, reflection, diffraction, dispersion, 

 polarization and applications to many optical instruments. 

 Complete with set of four concave and convex lenses, two 

 prisms, three mirrors (plane, concave and convex), etc. 



3677. DIVERGING RAY ATTACHMENT. By 



means of this attachment a diverging pencil of light may 

 be produced and the law^s of optics when using such a 

 pencil may be demonstrated. For use in connection with 

 the Optical Disc No. 3675. 



3680. SOURCE OF LIGHT for Optical Disc. 

 Avoids the necessity of a mirror to reflect sunlight in the 

 room, or of arranging an arc lamp or any temporary 

 light source. May be connected to any lamp socket. 

 Needs no attention and gives a beam of parallel rays suffi- 

 ciently strong to be shown to a claiss without a darkened 

 room and is a necessary accessory for using the optical 

 disc. 



We shall be pleased to send to science departments of schools outside of the. United 

 States our especially prepared catalog for foreign circulation only. A request giving- your 

 official position is all that is necessary in order to receive this catalog. 



W. M. WELCH SCIENTIFIC COMPANY 



Manufacturer, Importer and Exporters of ScientlficjApparatus 



1516 Orleans Street CHICAGO, ILL., U.S. A. 



