RECORDS 59 



The President stated the object of the meeting, and that a 

 notice had been sent by the Recording Secretary to all resident 

 members and fellows entitled to vote, in accordance with the 

 requirements of Section 5 of the amended charter. 



The proposed constitution, filed herewith,^ was then read by 

 the Recording Secretary, pro tern. , and on motion of Professor 

 R. S. Woodward, seconded by Professor Francis E. Lloyd was 

 unanimously adopted. 



The academy then adjourned. 



Richard E. Dodge, 



Recording- Secretaiy, pro teni. 



SECTION OF GEOLOGY AND MINERALOGY. 



April 24, 1902. 



Section met at 8:30 P. M., Professor J. J. Stevenson presid- 

 ing. The minutes of the last meeting of Section were read and 

 approved. 



The following program was then offered : 



Lea McI. Luquer, On the Determination of the Rela- 

 tive Refractive Indices of Minerals in Rock Sections by 

 THE Becke Method. 



Austin F. Rogers, The Minerals of the Joplin, Mo., 

 Lead and Zinc District. 



Summary of Papers. 



Lea McI. Luquer stated that in most schemes for the optical 

 determination of minerals in rock sections, the birefringence and 

 resulting interference colors are made the basis of the scheme of 

 classification. It is also desirable, however, to bring into con- 

 sideration an approximate knowledge of the indices of refrac- 

 tion, and where the relative differences in the indices of two ad- 

 joining minerals is required, the method devised by Becke is 

 found to be very convenient. This method depends upon the 

 principle of the total reflection of light, and with proper adjust- 

 ment of the microscope, which is to be focused sharply on the 



• See Appendix. 



