VI CONTENTS. 



PAGE 



XIII. On Satum^s Rings. By L. Trouvelot 191 



XrV. Supplementary Note on the Theory of the Horizontal Pho- 

 toheliograph. By Professor William Harkxess, 



U. S. NA\Tr 194 



XV. Researches on the Substituted Benzyl Compounds, By 



C. LoRiNG Jackson 202 



XVI. Remarks on the Brain, illustrated by the Description of the 

 Brain of a Distinguished Man. By Thomas Dwight, 



M.D 210 



XVII. Theory of Absorption-Bands in the Spectrum, and its 

 Bearing in Photography and Chemistry. By Dr. Rob- 

 ert Amory 216 



XVlll. Surfaces of the Second Order, as treated by Quaternions. 



By Abbott Lawrence Lowell 222 



XIX. On the Synonymy of some Species of Uredinece. By 



W. G. Farlow 251 



XX. Metasomatic Development of the Copper-bearing Rocks of 



Lake Superior. By Raphael Pumpelly .... 253 

 XXI. Investigations in Quaternions. By Washington Irving 



Stringham 310 



XXII. On a New Method for the Separation and Subsequent 

 Treatment of Precipitates in Chemical Analysis. By 



F. A. GoocH 342 



XXin. On Peirce^s Criterion. By Benjamin Peirce . . . 348 

 XXIV. Note on the Measurement of Short Lengths. By Leonard 



Waldo 352 



XXV. Contributions to the Botany of North America. By Asa 



Gray 361 



XXVI. Spherical Conies. By Gerrit Smith Sykes .... 375 

 XXVII. On the Influence of Internal Friction upon the Correction 

 of the Length of the Seconds^ Pendulum for the Flexi- 

 bility of the Support. By C. S. Peirce .... 396 



XXVIIL Color-Perception. By G. Stanley Hall 402 



XXIX. On the Intensity of Terrestrial Magnetism at Cambridge. 



By Henry Goldmark 414 



