A. W. Ewell — Rotatory Polarization. 36 7 



refraction and rotatory polarization may, however, be distin- 

 guished if the incident light is polarized in a number of 

 azimuths, for simple double refraction will rotate the plane of 

 polarization in one direction in some azimuths and in the 

 other direction in other azimuths, for it has nothing in its 

 nature to distinguish the two directions of rotation. In these 

 experiments the jelly was always under some strain and, 

 therefore, showed some double refraction. To eliminate the 

 effect of the double refraction, which increased the proper 

 rotation in some azimuths and decreased it in others, and also 

 to obtain greater accuracy, readings w T ere always made, by 

 means of the above mentioned gearing, in eight symmetrically 

 distributed azimuths, and every position of the analyzer or 

 rotation of the plane of polarization, given below, is the mean 

 of eight such readings. 



Natural Rotation of the Jelly. — The natural rotation of the 

 jelly (usually about 2°*7 per cm.) has been subtracted from the 

 observed rotation in every case and the rotation stated is the 

 difference due to the mechanical strain. 



To obtain constant definite results it was necessary to deter- 

 mine what other conditions besides the twist influence the 

 amount of the rotation. These conditions will now be con- 

 sidered in their approximate order of importance. 



Conditions Influencing Amount of Rotation. 



Lateral Envelope. — Aside from qualitative experiments with 

 glass, the only successful experiments described in previous 

 papers were with jelly in rubber tubes. It was very important 

 to determine whether independent cylinders gave this rotation 

 when twisted. I will give in full the last set of readings with 

 independent jelly cylinders which were made under what previ- 

 ous experience had shown to be the most suitable conditions. 

 The lower clamp was fixed by the clips, g, after the twist was 

 applied. As is shown later, it would have been better to have 

 had it hanging free, but these independent cylinders could not 

 support this weight under twist sufficient time for reading the 

 rotation. 



Independent jelly cylinders. 



July 12, '02. Initial position of the analyzer for uniform color 

 of the two halves of the biquartz = 94. 



Length (between rubber clamps) = 5 # l cm . Diam. = 2*1. 



1' delay after applying twist before making readings to avoid 

 relaxation disturbances (see below). 



Am. Jour. Sci.— Fourth Series, Vol. XV, No. 89.— May. 1903. 

 25 



