SCIENCE-ADVERTISEMENTS 



STRIINO EUBCTROMBTBR 



Made by the Cambridge Scientific Instrument Company, Ltd. 



This instrument, originally 

 suggested by Prof. Einthoven, 

 employs as the moving system, 

 a silvered quartz fibre tightly 

 stretched between, and parallel 

 to two fixed metal plates. 



It possesses the folldii>ing special features: 



1. Extremely rapid in action. 



2. It is a sensitive instrument with 

 a very small capacity (a few cm. 

 only). 



3. The sensitiveness can readily be 

 removed. 



4. The zero is stable. 



5. It can be used as a projection in- 

 strument, or as a recording instrument. 



Write for List 201 



1211-13 ARCH ST. 



JAMES G. BIDDLE 



Special Representative PHILADELPHIA, PA. 



When in Philadelphia be sure to viiit our Permanent Exhibit of scientific apparatus. 



Natural History Material 



ZOOLOGY MINEKALOQY 



We have been handling Natural History 

 Material of all kinds for the past fifty years, 

 and so have accumulated a very complete stock. 

 Our prices are as low as the quality of the 

 specimens will permit. We are constantly pre- 

 paring circulars and price lists covering our 

 material in the different branches, which we 

 will be pleased to send free of charge to the 

 readers of Science. 



Some of our recent circulars ; 



S-121 Rare Bird Skins 

 S-122 Mounted Bird Skins 

 S-98 Material for Dissection 

 S-123 Philippine Land SheUs 

 S-120 Special Minerals 

 S-110 Complete TrUobites 

 S-111 Jurassic Fossils 

 S-119 Cretaceous Fossils 



CONCHOLOQY 



QEOLOGY 



Ward's Natural Science 

 Establishment 



College Ave. Rochester, N. Y. 



GOODE'S BASE MAPS 



For classes in geography, geology, eco- 

 nomics, history, etc. 18 subjects. Two 

 sizes: SxlOJin., Ic; 15x10^ in., 3c; pos- 

 tage extra. Perforated for notebook ; suit- 

 able for ink or pencil. Samples on request. 



The University of Chicago Press 

 Chicago, Illinois 



JULIEN'S POWER AND FOOT LATHES 



Use of Geologists, Mineralogists, Petrographers, Met- 

 allurgists, Mining Engineers, in SLICING and 

 POLISHING all hard substances, rocks, etc., and in 

 preparation of MICROSCOPIC THIN SECTIONS. 



GUSTAVUS D. JULIEN 

 3 Webster Terrace NEW ROCHELLE, N. Y. 



OUR 1913 CATALOG # 



ContainB many new instruments, all A 

 new illustrationB, lowest prices and ^ 

 I valuable information of interest to every M 

 k science instructor. Send us your name ^ 

 and address and we will send you a free ^ 

 >copy. elffiBe Sales Dep't ^ 



* Chicago Apparatus Co., Chicago. III. 9 



