A. W. Ewell — Rotatory Polarization. 363 



Art. XXX YI. — Rotatory Polarization Mechanically Pro- 

 duced; by Arthur W. Ewell. 



Some four years ago Prof. A. W. Wright of Yale University 

 suggested to the author that he investigate the optical effects 

 of torsion upon transparent media, citing a reference of Yerdet* 

 to the unsuccessful attempts of F. E. Neumann and Drion to 

 obtain rotatory polarization by twisting. The results of the 

 author's investigation were given in a paper f published a year 

 later in which it was demonstrated that jelly in a rubber tube, 

 when subjected to severe twist, rotates in the opposite direc- 

 tion to the twist, the plane of polarization of polarized light 

 which traverses the jelly parallel to the axis of twist, and that 

 this rotation is a higher power of the twist than the first. In 

 a paperj published a year later it was shown that this rotatory 

 polarization was quite uniform over the cross section of a 

 jelly tube ; that it was present in an annular jelly tube formed 

 by pouring the jelly into the space between two rubber tubes 

 both of which were cemented to glass caps ; that a glass rod 

 twisted when heated to softness showed no rotatory polariza- 

 tion when allowed to cool ; and, finally, that glycerine, stirred 

 or twisted in rubber tubes, even at zero degrees showed no 

 rotatory polarization. 



The present paper describes experiments performed during 

 the past two years, in seeking definite quantitative relations 

 between the rotation of the plane of polarization and the twist 

 and twisting moment and what conditions besides the twist 

 influence the rotation. A great number of experiments were 

 make with several forms of apparatus which afterwards proved 

 to be merely preliminary. Only the final form of apparatus 

 and the experiments performed with it will be described. 



Material Used. 



Jelly. — The great majority of the experiments were made 

 with jelly, which is by far the best material which the author 

 has discovered, since it may be made very transparent, possesses 

 in a marked degree all the features of an elastic solid and 

 allows great distortion without serious injury to its optical or 

 mechanical properties. 



In the experiments described in former papers the jelly was 

 composed of choice calves foot gelatine and water. The jelly 

 used in the experiments described in this paper contained in 

 addition glycerine, which makes the jelly tougher and constant, 



*Verdet : Optique ii, p. 389. 



+ This Journal (3), viii, 89, 1899 ; also abstract in Phys. Zeitschrift, i, 

 No. 18. 



X Johns Hopkins University Circulars, June, 1900. 



