iv CONTENTS. 



Xn. Brief Contributions from the Physical Laboratory of Har- 

 vard College : — 



2. On a New Induction Coil. By John Trowbridge o81 



3. On the Effect of Armatures on the Magnetic State of 



Electro-Magnets. By B. O. Peirce and E. B. 

 Lefavour 385 



4. On the Time of Demagnetization of Soft Iron. By 



AV. C. HoDGKiNS AND J. H. Jennings . . . 387 



XIII. Contributions from the Physical Laboratory of the Mas- 



sachusetts Listitute of Technology : — 



2. Light transmitted hy one or more Plates of Glass. 



i3Y W. W. Jacques 389 



XIV. On the Application of Logical Analysis to Multiple Algebra. 



By C. S. Peirce 392 



XV. On the Uses and Transformations of Linear Algebra. By 



Benjamin Peirce 395 



XVI. Optical Notices. By Wolcott Gibbs, M.D. : — 



1. On a Neio Optical Constant 401 



2. On a Method of Measuring Refractive Indices with- 



out the Use of Divided Instruments 417 



XVII. Contributions from the Physical Laboratory of the Mas- 

 sachusetts Institute of Technology : — 



3. Intensity of Twilight. By Charles H. "Williams 421 



4. Light of the Sky. By W. O. Crosby .... 425 



5. Light absorbed by the Atmosphere of the Sun. By 



E. C. Pickering and D. P. Strange ... 428 



6. Tests of a Magneto-Electric Machine. By E. C. 



Pickering and D. P. Strange 432 



7. Ansicer to M. Jamin's Objections to Ampere'' s Theory. 



By William W. Jacques 445 



XVIII. Melanosiderite : A Neio Mineral Species., from Mineral 

 Hill, Delaware County, Pennsylvania. By Josiah P. 

 Cooke, Jr 451 



XIX. On Two Neio Varieties of Vermiculites, tcith a Revision of 

 the other Members of this Group. By Josiah P. Cooke, 

 Jr., and F. a. Goocii 453 



Proceedings ' 4G3 



Index 525 



