494 Mr. B. V. Hill on Accidental 



the cell were greased so that the ends could be slipped toward 

 each other. A solution containing i a gram in 100 c.c. 

 was put in the cell and allowed to stand for twenty-four hours. 

 On pressing the ends together in a direction perpendicular to 

 the path of the light, double refraction appeared and increased 

 till the plane of polarization had been rotated 0°'5. This 

 represented a relative retardation of "0028 X for sodium light. 

 When the motion was stopped, the double refraction remained 

 unchanged, showing that the strain was sustained, as in the 

 case of the stronger jellies. When, however, the distortion 

 was carried further the double refraction suddenly disappeared, 

 as if the substance had been ruptured and the strain released. 

 This solution, though acting thus like an elastic solid, was 

 nearly as fluid as water, flowing freely. 



A solution containing 3 grams to the litre was now put 

 into the chest of the apparatus used in the former experiments. 

 With a velocity of three revolutions per second there was a 

 rotation of the plane of polarization of o, 058, representing a 

 relative retardation of "000325 A. When the motion was 

 suddenly stopped, the field did not become uniformly bright 

 at once, but the shade swung across the centre and the other 

 side became dark. Two or more complete oscillations were 

 performed. The first time the shade went past the original 

 zero by 0°*05, representing '00029 A. 



In cases where this oscillation was not observed the double 

 refraction did not cease as soon as the motion stopped, but 

 required perhaps a tenth of a second to disappear. 



Balsam fir was put into the glass cell and the ends pressed 

 together as before. The plane of rotation was rotated 0°'2, 

 representing a relative retardation of 0'00112X. Here the 

 effect did not remain as in the case of thin jelly, but a slow 

 motion was required to maintain it. 



A flexible cell was made by putting wooden stoppers in the 

 ends of a piece of rubber hose. Glass ends were fastened in 

 these stoppers and oil placed in the cell and compressed, so 

 that the cross section was an ellipse. No effect of double 

 refraction could be seen, however. Any such effect which 

 may be present is doubtless too small for detection with the 

 present optical system. 



Crystalloids. 



By using as a source of light a ground-glass plate at the 

 focus of the lens which condensed the sun's rays, a sensibility 

 of O'OOOO 12 A was obtained. With this increased sensibility 

 water was examined, but no effect was obtained. 



With a solution of hyposulphite of soda the sensibility was 



