202 



SCIENCE. 



[N. S. Vol. XIX. No. 475. 



dent, E. H. Hall; secretary, Dayton C. 

 Miller, Case School of Applied Science, 

 Cleveland, Ohio; members of the sectional 

 committee, E. H. Hall, W. P. Magie, D. C. 

 Miller, D. B. Brace, A. G. Webster, G. F. 

 Hull and F. E. Nipher. 



Professor E. Eutherford, of McGill Uni- 

 versity, gave a popular scientific lecture on 

 'Kadiiun and Eadio-activity. ' The lecture 

 was illustrated with many experiments and 

 demonstrations, some exhibiting Professor 

 Rutherford's recent researches. The lec- 

 ture was greatly appreciated by the large 

 audience in attendance. 



The number of papers read at St. Louis 

 was thirty-six, twenty-four before Section 

 B, and twelve before the Physical Society. 

 Of these papers thirteen were upon elec- 

 trical subjects, eleven were optical, four 

 were upon heat, three upon radio-activity 

 and five were upon miscellaneous subjects. 

 The abstracts of the papers read before 

 Section B are given below; the papers 

 given before the Physical Society are de- 

 scribed in the report of that society. 



lieport of the Committee on the Velocity of 

 Light: D. B. Brace, University of Ne- 

 braska. 



A Half-Shade Elliptical Polarizer and 

 Compensator: D. B. Beace, University 

 of Nebraska. 

 To be published in full in the Physical 



Revieiv. 



On the Effect of a Magnetic Field on the 

 Interference of Natural Light: John 

 Mills, University of Nebraska. 

 The conception of natural light as an 

 elliptical vibration and our knowledge of 

 the Faraday 'effect' would give as a cri- 

 terion for an analogous rotation of natural 

 light, the disappearance of interference 

 fringes, previously observable, upon the 

 formation of a magnetic field capable of 

 rotating plane polarized light through an 



angle of an odd multiple of 90°. The ap- 

 paratus consisted of a Michelson inter- 

 ferometer. In the path of each beam was 

 placed a tube of carbon disulphide sur- 

 rounded by a solenoid. Natural mono- 

 chromatic light was used and the current 

 varied. Observations were taken at the 

 points of disappearance and reappearance 

 of the fringes. The mean of these cur- 

 rent readings was taken as that for which 

 interference was impossible. These values 

 of the current would have produced in 

 plane polarized light a rotation of 95.8°, 

 256.8°, 447.5°, 613.6°. 



The apparent invalidation of the results 

 obtained because of a partial polarization 

 of the entering light by the reflecting sur- 

 faces is also discussed. 



On the Velocity of Light in a Magnetic 



Field: John Mills. 



The experimenter undertook to measure 

 the acceleration or the retardation ex- 

 perienced by a circular component travers- 

 ing a magnetic field. The apparatus con- 

 sisted of a Michelson interferometer. In the 

 path of each beam was placed a tube of 

 carbon disulphide surrounded by a solenoid. 

 The light passed through a Nicol prism and 

 a Bravais double plate. Half of the fringes 

 were thus composed of light circularly 

 polarized in a direction opposite to those 

 of the other half. The formation of a 

 magnetic field produced a shifting of the 

 two sets in opposite directions. The cur- 

 rent causing a shifting of one full band 

 (corresponding to a difference in phase of 

 360°) was observed. On the assumption 

 that the rotation of plane polarized light 

 is the result of a difference of phase be- 

 tween its circular components, produced by 

 an acceleration of one component and a 

 corresponding retardation of the other, the 

 difference of phase corresponding to this 

 value of the current was calculated. It 

 was 368°. The readings for the current 



