PROCEEDINGS 



OF THE 



American Philosophical Society 



HELD AT PHILADELPHIA 



FOR PROMOTING USEFUL KNOWLEDGE 



Vol. LI. October-November, 191 2. No. 207. 



CONTENTS 



The Formation of Coal Beds. IIL By John J. Stevenson - - 423 

 An Autocollimating Mounting for a Concave Grating. By Horace 



Clark Richards _ . . 554 



The Objective Prism. By Edward C. Pickering - - - - 564 

 Relations between the Spectra and Other Characteristics of the Stars. 



By Henry Norris Russell - - - - - - - 569 



Some Former Members of the American Philosophical Society. By 



Thomas Willing Balch _ . 580 



Obituary Notices of Members Deceased. 



Jules Henri Poincare - - -- - - --iii 



Stated Meeting, October 4 - - - - - - -— - xvii 



Stated Meeting, November j-------- xix 



Stated Meeting, December 6 - - - - - - - - xix 



PHILADELPHIA 



THE AMERICAN PHILOSOPHICAL SOCIETY 

 104 South Fifth Street 



1912 



