474 PROCEEDINGS OF THE AMERICAN ACADEMY 



Professor W. Watson presented a copy of his work on 

 " Descriptive Geometry " to the Academy. 



Prof. Asa Gray presented, by title, a paper, " A Con- 

 spectus of the North American HydrophyHacese." 



Mr. Sereno Watson presented, by title, a paper on the 

 " Revision of the Genus Ceanothus, and Descriptions of New 

 Plants, with a Synopsis of the Western Species of Silene.'' 



Dr. W. G. Farlow presented, by title, a paper on the Algse 

 of the United States. 



Six hundred and seventy-ninth Meeting. 



April 13, 1875. — Monthly Meeting. 



The President in the chair. 



Professor Wolcott Gibbs communicated the following 

 " Optical Notices : " — 



1. On a New Optical Constant. 



2. On the Determination of Indices of Refraction without 

 the use of Divided Instruments. 



3. On a New Optical Instrument. 



Professor John Trowbridge read a paper, " On a New 

 Form of Induction Coil." 



Professor Trowbridge also communicated two papers from 

 the Physical Laboratory of Harvard College, by undergrad- 

 uates of the University : — 



1. On the Effects of Armatures upon Electro-Magnets, by 

 B. O. Peirce and E. B. Lefavour. 



2. On the Time of Demagnetization of Soft Iron, by W. C. 

 Hodgldns and J. H. Jennings. 



The Recording Secretary presented, by title, a paper, " On 

 the Light transmitted through one or more Plates of Glass," 

 by W. W. Jacques. 



