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L. Note on Accidental Double Refraction in Liquids. By 

 Bruce V. Hill, A.M., Former Fellow in Physics* Univer- 

 sity of Nebraska *. 



IN a former paper f the writer gave the results of a series 

 of experiments upon solutions of gelatine and gum- 

 arabic in water. These solutions were subjected to a strain 

 by being placed between two parallel rotating cylinders. 

 When the cylinders were set in motion the liquids became 

 double- refracting. In the case of gelatine this double- 

 refraction increased to a maximum, then decreased, changed 

 sign, and finally increased in the opposite direction. The 

 solutions of gelatine were then placed under a static strain, 

 and were still found to become double-refracting. This 

 strain was maintained by a solution having only *5 gm. of 

 gelatine in 100 c.c. of water. Although these dilute solu- 

 tions when examined in a test-tube seemed as perfectly 

 mobile as water, it appeared from the above that they were 

 not true solutions, but quasi-solid substances capable of sus- 

 taining only very small strains without rupturing, and further 

 experiments upon them seemed necessary. 



To examine jellies too dilute to bear their own weight they 

 were placed in thin-walled brass tubes. These tubes were 

 42*55 cm. in length and 2*77 cm. in diameter. To the ends 

 of these tubes glass caps were fastened by slipping short 

 pieces of rubber-hose over them. The tubes were strained, 

 so that their cross- section was elliptical, by means of clamps. 

 The effect of double-refraction decreases so rapidly with rise 

 of temperature that at room temperature — about 23° C. — no 

 effect was visible in the dilute jellies. The tubes were then 

 surrounded by ice, and the formation of dew on the glass 

 ends w r as obviated by slipping over the tube a second one, 

 also having a glass cap and containing a little phosphoric 

 anhydride. 



With tubes of this length it was very difficult to make the 

 compression uniform throughout, but with shorter tubes the 

 distortion had to be carried beyond the limits of perfect 

 elasticity of the jellies in order to obtain a measurable 

 effect. 



The amount of double-refraction was measured as before 

 by means of a half-shade polariscope. With jellies contain- 

 ing *3 gm. (or less) of gelatine in 100 c.c. of water, the 

 optical sensibility was o, 005 of rotation of the plane of 

 polarization or '000028 X relative retardation of the two 



* Communicated by Prof. D. B. Brace. 

 + Phil. Mag. Dec. 1899. 



