H^\^~ PROCEEDINGS 



AMERICAN PHILOSOPHICAL SOCIETY 



HELD A I PHILADELPHIA 



FOR PROMOTING USEFUL KNOWLEDGE 



Vol. XLIV. May-July, 1905. No. 180. 



CONTENTS. 



The Mutual Affinities of the Species of the Genus Cambarus, 

 and their Dispersal over the United States. By Dr. A. 

 E. Ortmann 91 



The L T se of the Rotating Anode and Mercury Cathode in 

 Electro- Analysis. By Lily G. Kollock and Edgar F. 

 Smith 137 



Observations on Columbium and Tantalum. By Edgar F. 



Smith 151 



Enquiry into the Pressure and Rainfall Conditions of the Trades- 

 monsoon Area. By W. L. Dallas 159 



The Relation Between the Economic Depth of a Bridge Truss 

 and the Depth that Gives Greatest Stiffness. By Mans- 

 field Merriman 164 



On the Use of the Falling Plate Oscillograph as a Phase Meter. 



By William McClellan 166 



Some Observations on Columbium. By Roy D. Hall and 



Edgar F. Smith 177 



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1905 



