Double Refraction in Carbon Disulphide 3 



Nicoi N, covered half of the field and was placed with its princi- 

 pal axis at an aximuth of forty-five degrees to the plane of vibra- 

 tion of the polarized light. The edge of this strip was parallel to 

 the faces of the electrodes, thus making the vanishing line par- 

 allel to the greatest dimension of the field of view. When elec- 

 trodes of greatest length (127 an.) were used, this strip was 

 placed between the compensator and the analyzer,, as the distance 

 was too long to give good definition. The second section, the 

 "compensator" C (fig. i), was placed next to the analyzing 

 Nicol N', and covered the whole field. This section was mounted 

 on a circle with a vernier that could be read to minutes. The 

 position of the strip was changed several times, so that readings 

 were obtained from different parts of the circle and thus elim- 

 inated any possible instrumental errors. 



JE'A /P TJY 



A forty-eight candle power Nernst "glower," one centimeter 

 long and one millimeter in diameter, was first used as light-source 

 L (fig. i). Later, observations were taken with sunlight passed 

 through a spectroscope and observations were taken for red 

 (620 fjifj.), green (540 /x/i,), and blue (490 /x/a) light. By means 

 of a condensing lens A (fig. i) the light was passed through the 

 polarizing Nicol, the "sensitive strip," the liquid between the 

 plate electrodes E (fig. i), through the compensator, analyzer, 

 and thence to a focus O within the observer's eye. When sun- 

 light was used the light was strong enough to allow the use of a 

 short focus telescope with small magnifying power placed next 

 to the analyzer. One of the electrodes was grounded and the 

 other connected to the storage battery. F is a voltmeter, con- 

 nected across the electrodes. 



