OF ARTS AND SCIENCES. 335 



The following papers were presented by title : — 

 Contributions to American Botany: I. Additions to the 

 Flora of Western North America. II. Descriptions of New 

 Species of Plants collected in Mexico, chiefly by Mr. C. G. 

 Pringle, in 1889 and 1890. By Sereno Watson. 



Contribution from the Herbarium of Harvard University : 

 Descriptions of New Plants, chiefly Mexican Gatnopetalce, 

 collected by Mr. 0. G. Pringle in 1889 and 1890. By B. L. 

 Robinson. 



Eight hundred and forty-second Meeting* 



May 13, 1891. — Monthly Meeting. 



The President in the chair. 



The following papers were presented by title : — 



On some Theorems which connect together certain Line 

 and Surface Integrals. By B. O. Peirce. 



On some Cases of Electrical Flow in Thin Conductors. 

 By B. O. Peirce. 



The Quantitative Determination of Arsenic by the Marsh- 

 Berzelius Method, especially as applied to the Analysis of 

 Wall Papers and Fabrics. By Charles R. Sanger. 



On the Products obtained by the Action of Nitric Acid 

 upon Bromtrinitrophenylmalonic Ester. By C. Loring Jack- 

 son and W. B. Bentley. 



Note on Tribrommononitrobenzol. By C. Loring Jackson 

 and W. B. Bentley. 



On the Structure and Development of Choreocolax Poly- 

 siphonisB, Reinsch. By Herbert M. Richards. 



Professor Edwin H. Hall gave an exposition of his thermo- 

 electric method for the study of cylinder condensation in 

 steam-engines. The apparatus, provided for by an appropri- 

 ation from the income of the Rumford Fund, was exhibited. 



