Vlll CONTENTS. 



Page 

 XL Note on the Representation of Orthogonal Matrices. By 



Henry Taber 163 



XII. Descriptions of New Plants collected in Mexico by C. G. 

 Pringle in 1890 and 1891, with Notes upon a few other 

 Species. By B. L. Robinson 165 



XIII. On Certain Products of the Dry Distillation of Wood: 



Methylfurfurol and Methylpyromucic Acid. By Henry 



B. Hill and Walter L. Jennings 186 



XIV. On Certain Derivatives of Pyromucamide. By Charles 



E. Saunders 214 



XV. On the Least Number of Vibrations necessary to determine 

 Pitch. By Charles R. Cross and Margaret E. 

 Maltby 222 



XVI. The Tropical Faunal Element of our Southern Nymphalinm 



systematically treated. By Samuel H. Scudder . . 236 



XVII. Trianilidodinitrobenzol and Certain Related Compounds. 



By C Loring Jackson and H. N. Herman . . 252 



XVIII. Preliminary Communication on the Host oj Nectonema Agile, 



Verr. By Henry B. Ward 260 



XIX. On the Thermal Conductivity of Cast Iron and of Cast Nickel. 



By Edwin H. Hall 262 



XX. On some Experiments with the Phonograph, relating to the 

 Vowel Theory of Helmholtz. By Charles R. Cross 

 and George V. Wendell 271 



XXI. The Reactions of Sodic Alcoholates with Tribromtrinitrobenzol. 

 Second Paper. By C. Loring Jackson and W. H. 

 Warren 280 



XXII. On the Action of Water upon Tribromtrinitrobenzol and Tri- 

 bromdinitrobenzol. By C. Loring Jackson and W. H. 

 Warren . . . 317 



