VUl 



SCIENCE— ADVERTISEMENTS 



L 101 Student's Spectrometer 



American manufacture of modern design embodying all the well known 

 qualities of Gaertner workmanship 



Used By Educational Institutions Throughout The World 



For full information write for Catalogs "L" and "M" 



High Grade Physical Apparatus for Elementary and Advanced Courses 



WM. GAERTNER & CO. 



5343 Lake Park Avenue 



Chicago, Illinois 



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 — 

 believing ii to be superior to a?iy 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. 



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

 IG r t«()-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 

 J^ H.P. motor — all mounted together 

 on one base. 

 Write for descriptive bulletin S-965 



JAMES G. BIDDLE 



1211-13 Arch St. PhUadelphia 



