SCIENCE-ADVERTISEMENTS 



Electrical Measuring Instruments and 

 Laboratory Apparatus 



Made by SIEMENS & HALSKE 



When considering the purchase of alternating or 

 direct current voltmeters, ammeters, wattmeters, 

 transformers, etc., etc., it is well worth while to 

 investigate the magnificent line of such instru- 

 ments made by Siemens & Halske. 



Besides electrical measuring instruments this Firm 

 also offers a distinctive line of laboratory appara- 

 tus, including oscillographs, iron testing equip- 

 ment, resistance boxes, bridges, induction stand- 

 ards, high frequency machines, galvanometers, etc. 



Advise what your needs are and we will submit 

 necessary data. Write for catalog 770 — "Pre- 

 cision Electrical Measuring Instruments. " 



SIEMENS & HALSKE PRECISION VOLT-AMMETER 



JAMES G. BIDDLE 



1211-13 ARCH ST. Sole Agent for United states PH I LADELPH I A, PA. 



When in Philadelphia be sure to visit our Permanent Exhibit of Boientific apparatus 



The name "LEITZ" on a microscope proclaims it an instrument of precision recognized by the 

 foremost authorities throughout the world. 



ERNST LEITZ 



"Leitz Prism Binoculars" 



are built under the same standard of precision — 

 they are scientific intruments of the highest order. 



The double acting focussing arrangement with 

 the new form of oil packing make them dust and 

 moisture proof. 



The fact that the Leitz Prism Glasses are 

 the standard of the U. S. Naval Observa- 

 tory, U. S. Army, V. S. Navy, and U. S. 

 Geological Survey, and have been selected 

 for important Intertropical and Arctic Sci- 

 entific Exploration Expeditions is the best 

 recommendation we can offer. 



Leitz Prism Binoculars are made for scientific 

 work, sports, hunting and theatre. 



Educational Institutions can import them tree 

 of duty. 



Special prices to instructors. 



Write for Descriptive Literature 44 J.-Y. 



30 East J 8th Street 

 NEW YORK 



