SCIENCE— ADVERTISEMENTS 



Visual Instruction 



WITH 



Spencer Delineascope 



MODEL 3 



is made perfect because it is an IDEAL 

 STEREOPTICON for both lantern slides and 

 opaque objects, such as pictures, post cards, 

 reading matter and objects of all kinds, dead 

 or alive. 



IDEAL because it embodies basic ideas 

 (Patented) possessed b}' no other. Example: 

 Mechanical means of handling the slides, 

 which does awaj' with the old antequated 

 lantern-slide holder and at the same time 

 gives a "dissolving effect" on the screen, 

 unattained with other outfits except by using 

 two Stereopticons, one above the other. 



One Spencer Delineascope does it 



New Booklet KllJuit Ready 



Spencer DeliDeaacop*, Ua^*! 3, for both lantern slides 



and opsque objects 



100 Watt Mazda bulb illnmlnant. Price, $150.00 



SPENCER LENS COMPANY 



BUFFALO. N. Y. 



MANUFACTURERS OF 



MICROSCOPES, MICROTOMES, DELINEASCOPES 



OPTICAL GLASS, SCIENTIFIC APPARATUS, ETC. 



Langmuir High-Vacuum Pump 



Dr. Irving Langmnir (of the 

 General Electric Co.) has de- 

 veloped an exceedingly inter- 

 esting and valuable Aig/i-speei/ 

 high-vacuum pump, and by 

 special agreement with the 

 makers, we are acting as sole 

 distributors, for laboratory 

 purposes. 



With this pump pressure as 

 low as lO"" bar have been ob- 

 tained ; and there is little 

 doubt that very much lower 

 pressures can be produced, by 

 cooling the bulb to be ex- 

 hausted, in liquid air, so as 

 to decrease the rate at which 

 gases escape from the walls. 



Some type of primary pump 

 must be used ; capable of de- 

 veloping a vacuum not less 

 than 0. 1-0.15 mm.of mercury. 

 The illustration shows a Langmnir pump, connected to a two-stage primary oil pump — which is op- 

 erated by a J HP motor ; all three parts of the outfit being assembled together on one base. 



JAMES G. BIDDLE 



1211-13 ARCH STREET 

 PHILADELPHIA 



If interested, write for copy of illustrated 

 Bulletin 881, issued November, 1917 ; 

 and also copy of paper by Dr. Langmuir. 



