SCIENCE-ADVERTISEMENTS 



Laboratory Apparatus 



made by 



SPINDLER & HOYER 



standard Batter} lor Electrostatic Measurements 



This battery is made according to designs 

 of Prof. F. Krueger and is specially suited for 

 charging electrometer needles, and standard- 

 izing electroscopes. 



List 36 (32 pages) describes several sizes 

 of this battery, and also Electrometers for 

 Radioactive Measurements, Apparatus for 

 Measuring Specific Electric Conductivity of 

 Air, Condensers for Investigating Xray Ioniza- 

 tion, Meteoroscopes, Seismographs, etc., etc. 



List 37 (4 pages) is devoted to a New 

 Portable A pparatus for Psychological Eeaotion 

 Examinations. This is a simple but quite 

 complete outfit and is well adapted for associa- 

 tive examinations in applied psychology. 



List 35 (6 pages) tells of the Hydrody" 

 namic Instruments according to Prof. V- 

 Bjerknes, which are admirably adapted for 

 illustrating various electrical and magnetic 

 phenomena. 



All of these lists are of recent date and we 

 are prepared to supply copies to interested 

 scientists. 



Please let us know which ones you wish, 

 and also state what instrument equipment you 

 are interested in so that we may forward full 

 data. 



JAMES G. BIDDLE 



Special U. S. Representative 



1211-13 Arch Street 

 PHILADELPHIA 



When in Philadelphia be sure to visit our Permanent 

 Exhibit of Scientific Apparatus. 



DR. GAEDE'S 



MOLECULAR AIR 



PUMP 



A newLhigh vacuum pump which removes all vapors as 

 well as gases. Will exhaust a 6 liter flask, starting with 

 a pressure of 10 mm. to .00001 mm. in 3 minutes. Is built 

 on an entirely new principle, being without piston of any 

 kind, and the communication between the receiver and 

 the primary vacuum through the grooves and channels 

 of the pump is at no time closed. The movement of the 

 rotor acts on the movement of the gas molecules in the 

 grooves of the rotor or the casing and produces a vacuum 

 containing fewer molecules, i. e. a vacuum at the suction 

 nozzle of the pump. 



We also furnish the Gaede BUgh Vacuum Pump, and the 

 Gaede Rotary Pump for use as an auxiliary with either 

 the Molecular or High Vacuum Pump. 



Send for;complete descriptive pamphlets 



ARTHUR H.THOMAS CO. 



importers and Dealers 



MICROSCOPES, LABORATORY AP- 

 PARATUS AND CHEMICALS 



West Washington Square, 

 PHILADELPHIA 



