SCIENCE-ADVERTISEMENTS 



THE BROOKS' INDUCTOMETER 



In the Brooks' Inductometer is offered 

 a compact form of variable inductance, 

 with a self inductance range of 5 to 50 miUi- 

 henrys, possessing the following advan- 

 tages: 



1. A fair degree of astaticism, which 

 tends to eliminate errors due to stray 

 field effects. 



2. It is less expensive and at the 

 same time fully as accurate as the Ayrton- 

 Perry instrument. 



3. It occupies less space than the 

 Aryton-Perry form. 



The instrument has a very nearly uniform scale, obtained by properly proportioning the coils. 



It may be used as a mutual inductance. 



It has a good ratio of maximum to minimum inductance (about 9 to 1) and also has as high 

 a time constant as is consistent with good design and moderate size. 



The instrument is fully described in Bulletin No. 152, a copy of which will be sent upon request. 



THE LEEDS 8c NORTHRUP CO. 



ELECTRICAL MEASURING INSTRUMENTS 



4921 STENTON AVENUE PHILADELPHIA 



Langmuir Condensation Pump 



Dr. Irving Laogmnir (of the 

 General Eleotrio Co.) has de- 

 veloped an exceedingly inter- 

 esting and valuable high-speed 

 high-vacuum pump, and bj 

 Bpeoia! agreement with the 

 makers, we are acting as sole 

 distributors, for laboratory 

 purposes. 



With this pump pressure as 

 low as 1U~* 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 i UP motor ; all three parts of the outfit being assembled togttber 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. 



