SCIENCE-ADVERTISEMENTS 



zi 



Siemens & Halske 



Repair Shop 



Testing, Calibrating and Repair 



of Electrical Apparatus and 



Instruments 



Building: and Designing of Special 

 Apparatus for Scientific Investi- 

 gation and Experiments 



New York City 90 West Street 



Natural History Material 



ZOOLOaY MINERALOaY 



We have been handling Natural History 

 Material of all kinds for the past fifty years, 

 and so haye 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-lZl Rare Bird Skins 

 S-122 Mounted Bird Skins 

 S-98 Material for Dissection 

 S-123 Pliilipplne Land SlieUs 

 S-120 Special Minerals 

 S-nO Complete TrUobites 

 S-IU Jurassic Fossils 

 S-119 Cretaceous Fossils 



CONCHOLOQY 



aEOLOQV 



Ward's Natural Science 

 Establishment 



College Ave. Rochester, N. Y. 



Q=R Laboratory 

 Rheostats 



Types and Sizes 



G-E Laboratory Rheostats are made in five 

 types and thirty-six diflferent sizes, with num- 

 erous current capacities and resistances in each 

 size. 



Uses 



These rheostats have been found useful for 

 the following purposes: 



Switchboard Work Meter Testing 



Work in Standards Laboratories 



General Laboratory Work 



Wireless Work 



In the latter case, windings are non-inductive 

 and free from capacity. 



Some of the Users 



The list of users of G-E Eheostats includes 

 Universities, Colleges, Technical Schools, In- 

 dustrial Companies, Makers of Electrical In- 

 struments, and Departments of the tJ. S. 

 Government (including the Bureau of Stand- 

 ards). 



Write for illustrated descriptive catalog 781 



JAMES G. BIDDLE 



1211-13 Arch Street 

 PHILADELPHIA 



When in Philadelphia be sure to visit our Permanent 

 Exhibit of Scientific InBtniments. 



