PROCEEDINGS 



OF THE 



American Philosophical Society 



HELD AT PHILADELPHIA 



FOR PROMOTING USEFUL KNOWLEDGE 



Vol. L. January-April, 191 i. No. 198. 



CONTENTS. 



The Formation of Coal Beds, I. By John J. Stevenson i 



The Transpiration of Air through a Partition of Water. By C. Barus 117 



Elliptic Interference with Reflecting Grating. By C. Barus 125 



On the Totality of the Substitutions on n Letters Which are Commutative with 



every Substitution of a Given Group on the Same Letters. By G. A. 



Miller 139 



Obituary Notices of Members Deceased 



Henry Charles Lea iii 



PHILADELPHIA 

 THE AMERICAN PHILOSOPHICAL SOCIETY 



104 South Fifth Street 

 1911 



