SCIENCE-ADVERTISEMENTS 



New High Vacuum 

 Piston Pump 



Made by 



E LEYBOLD'S NACHFOLQER 



The Gaede His'i ^ iciniin 1 i t I'lnup, ■ 

 at the receut exliihituui jt the Aiiiericiiu Physical 

 iSooiety Id \Vaaliin_ton, miy be eisily driven by 

 baod, and requires no aiixiliaiy pump. 



It will evacuate a moderate sized X-ray tube 

 from atmospheric pressure nntil it gives off hard 

 X-rays in less than two minutes, vpithout the use of 

 drying tubes. Accessory apparatus is fitted directly 

 to the standard ground nozzle, thereby avoiding 

 rubber connections. 



It will be found useful in lecture rooms, for 

 demonstration purposes, and in experiments requir- 

 ing high vacua, as a number of striking phenomena, 

 which cannot be obtained inclosed tubes, can easily 

 be realized with the aid of this pump. 



Write for List VII, containing complete 

 description 



JAMES G. BIDDLE 



Manufacturer's Special 

 Agent 



1211-13 Arch St. PHILADELPHIA 



Be sure to visit onr Permanent Exhibit of 

 Scientific Instruments 



Moscow Natural Eye Model 



Pat. Feb. 3. 1914. 



A New and Valuable Aid in Feachins Anatomy and 

 Physioloey of the Eye 



These models consist of a real, natural eye 

 which has been hardened and fixed; then sectioned 

 in half and mounted in a glaes cell so as to show all 

 the internal parts of the eyeball. Tht'&e structures 

 are all held in their normal positions, and may be 

 easily dentified by means of the diagrammatic cut, 

 keyed to model, which accompanies each one. 



"Ihe Moscow Natural Eye Models are excellent 

 prepaviitions. Wefind them to be a great help in 

 laboratiry work, in Zoology, Physiology, Anatomy, 

 etc., etc ,'' Dr. J. E. Wodseda'lek, Professor of Zoology, 

 University o' Idaho. 



Mounted in ebonized box with hinged cover, 

 which protects the piass cell from injury. Absolute- 

 ly permanent, and fully guaranteed. 



Send for descriptive literature. 

 Manufactured by 



MOSCOW OPTICAL COMPANY 



MOSCOW. IDAHO 



Just 'Published 



PRINCIPLES OF 



S 



BY 



AMADEUS W. GRABAU, S.M..S.D. 



PROFESSOR OF PALAEONTOLOGY IN 

 COLUMBIA UNIVERSITY 



Large Octavo, 1150 pages, with 264 Illustrations In the text. 

 Cloth bound, price, 87.50. 



Send for descriptive circular 



A. G. SEILER & CO. 



PUBLISHERS 

 1224 Amsterdam Avenue NEW YORK. N. Y. 



