1896.] Proceedings of Scientific Societies. 437 



(a.) the curve representing a line of force proceeding from a system 

 consisting of two parallel electrified lines, is the locus of the intersec- 

 tion of two straight lines, rotating in the same plane about these two 

 parallel lines as axes with uniform but different angular velocities, 

 (b.) the curve representing a line of force proceeding from a system 

 consisting of two electrified points, is the locus of the intersection of 

 two straight lines, rotating, in the same plane about parallel axes 

 passing through those points, in such a manner that the versines of 

 their angles of inclination to the plane of the axes change at uniform 

 but different rates. 



April 20th.— Dr. C. M. Woodward presented the results of a study 

 of certain statistics of school attendance, from which it appeared that 

 the average age of withdrawal from the public schools in three cities 

 compared was, as follows : Boston, 15.8 ; Chicago, 14.6 ; St. Louis, 13.7. 



Professor J. H. Kinealy exhibited and gave a mathematical discus- 

 sion of the Stang planimeter, an interesting and simple instrument of 

 Danish invention, but improved in the United States. 



William Trelease, Recording Secretary. 



U. S. National Academy of Sciences.— April 21,1896.— The 

 following papers were read : The Geological Efficacy of Alkali Car- 

 bonate Solutions, E. W. Hilgard ; On the Color Relations of Atoms, 

 Ions and Molecules, M. Carey Lea; On the Characters of the Otocceli- 

 dae, E. D. Cope ; Exhibition of a Linkage whose motion shows the 

 Laws of Refraction of Light, A. M. Mayer; Location in Paris of the 

 Dwelling of Malus, in which he made the discovery of the Polarization 

 of Light by Reflection, A. M. Mayer ; (1) On Experiments showing 

 that the X-Rays cannot be Polarized by passing through Herapathite ; 

 (2) The Density of Herapathite; (3) Formula? of Transmission of the 

 X-Rays through Glass, Tourmaline and Herapathite, A. M. Mayer; 

 On the X-Rays from a Statical Current produced by a Rapidly Revol- 

 ving Leather Belt, W. A. Rogers and Frederick Brown ; Biographical 

 Memoir of James Edward Oliver, G. W. Hill ; Biographical Memoir 

 of Charles Henry Davis, C. H. Davis ; Biographical Memoir of George 

 Engelmann, C. A. White ; Legislation Relating to Standards, T. C. 

 Mendenhall; On the Determination of the Coefficient of Expansion of 

 Jessop's Steel, between the limits of 0° and 64° C, by the Interferen- 

 tial Method, E. W. Morley and W. A. Rogers ; On the Separate Meas- 

 urement, by the Interferential Method, of the Heating Effect of Pure 

 Radiations and of an Envelope of Heated Air, W. A. Rogers ; On the 

 Logic of Quantity, C. S. Peirce ; Judgement in Sensation and Percep- 

 tion, J. W. Powell ; The Variability in Fermenting Power of the Colon 



