SCIENCE— ADVERTISEMENTS 



"BECBRO" 



RHEOSTATS FOR EVERY CIRCUIT 



Tubular, Stone and Carbon Compression Types 



Send for Bulletin C-10 which shows many types of rheostats 

 made by us. 



BECK BROS. 



3640-42 N. Second Street Philadelphia, Pa., U. S. A. 



HIGH VACUUM PUMPS 



Whenever in lecture-room or laboratory practice, really high 

 vacuum is required, we recommend the Condensation Pump devel- 

 oped by Dr. Irving Langmuir of the General Electric Company — believ- 

 ing it to be superior to any other as yet obtainable. 



The Langmuir Pump operates with surprising rapidity, and there 

 seems to be no practical limit to the degree of exhaustion that can be 

 produced. 



M Some form of auxiliary pump must be used; and for that purpose 



\ we offer a special G.E. two-stage oil-sealed mechanical pump, which 

 .' is capable of producing a vacuum of 



' - " „ _ o.ooi mm. when used alone. 



The picture shows a complete out- 

 fit comprising Langmuir Condensation 

 Pump, two-stage auxiliary pump and 

 V2 H.P. motor — all mounted together on 

 one base. 



Write for descriptive bulletin S-p6s 



JAMES G. BIDDLE 



1211-13 Arch St.. Philadelphia 



