SCIENCE-ADVERTISEMENTS 



Source of 

 Light 



for the 



Optical Disc 



3680 3677 



367s 



Originated and developed in \M%%^^ Laboratories 



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Necessary for demonstrating the phenomena shown by the Opti- 

 cal Disc. Does not require waiting for sun to shine so as to 

 put up mirror to reflect it into the room. I^o need to pro- 

 vide a temporary set up of a light which gives only partially 

 parallel rays. 



Convenient to adjust as to height. May be tilted at an angle for 

 refraction tank, etc. May be attached to any lamp socket. 



CONCENTRATED FILAMENT NITROGEN LAMP 



Standard in Modern Projection Apparatus 



Needs no adjusting 



Noiseless 



No excessive heat 



(xives parallel rays 



Visible to entire class 



When bulb burns out a new one may be 



obtained from any garage 



aUALITY 



A Sign of Quality WjS IL(D 



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A Mark of Service 



W. M. WELCH SCIENTIFIC COMPANY 



Manufacturers, Importers and Exporters of 

 Laboratory Apparatus and School Supplies 



1516 Orleans Street 



Chicago, m., U. S. A. 



