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Scientific Intelligence. Ill 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1- Rotation of the Plane of Polarization produced hy the Gahanic 

 Current, — Wiede3ianw has presented a memoir upon this subject which 

 IS of special interest and importance from its containing the results of 

 the only series of quantitative experiments with which science has 

 been enriched. The apparatus employed was similar in principle to 



V( that used by Bloch in his determinations of the power of rotation of 



rock-crystal with reference to the fixed lines of the spectrum. A ray 

 of light was introduced into a dark room by means of a heIios!at, and 

 after passing through a narrow vertical slit traversed the polarizing 

 apparatus which consisted of two Nicol's prisms, the first fixed, the 

 second moveable round its axis and carrying a vernier applied to a 

 graduated circle and reading to 5'. Between the two NicoPs prisms 

 "Was placed the substance to be examined. Behind the second Nicol, 

 at a distance of from 6 to 8 feet, was placed a Galilean telescope mag- 

 iiifying about 15 times, and in front of the objective of this, a flint 

 glass prism which received the rays which had traversed the polarizing 

 apparatus. Under these circumstances the light was polarized by the 

 first Nicol in a definite plane which by the action of the interpolated 



*.s^ substance received an angular deviation, and this deviation was of 



course different for rays of different colors ; the second Nicol then 



I extinguished that color the plane of polarization of which was perpen- 



dicular to the plane of vibration of the Nicol. The spectrum formed 

 by the flint-glass prism and observed through the telescope exhibited 

 therefore only those colors which had passed through the polarizing 

 apparatus, and these with a greater or less brightness according as their 

 plane of vibration was less or more Inclined to the plane of vibration 

 of the second Nicol. In place of the color extinguished by this last, a 

 black band was seen in the spectrum : when the second Nicol is turned 

 round this band wanders from one end of the spectrum to the other, as 

 *be plane of vibration of the Nicol becomes successively perpendicular 

 ^0 the planes of polarization of the different colors. In the unextin- 

 guished portion of the spectrum the lines of Fraunhofer were distinctly 

 y ^0 be seen ; the cross-wires of the telescope were then brought to 



coincide with one of these lines, and then the second Nicol turned till 

 Ihe dark band in the spectrum coincided vyith the wires and conse- 

 quently also with the fixed line selected ; the angle through which the 

 •Nicol had been turned gave then the angle of rotation corresponding 

 to the given fixed line. In this manner it was easy to determine the 

 ^ngle of rotation for the different wave lengths corresponding to the 

 '»nes B, C, D, E, b, F and G, as had been done by Bloch for plates of 

 ro^k crystal. To test the accuracy of the method, oil of lemon and 

 Q'fferent kinds of oil of turpentine were examined ; the results reduced 

 ^0 lengths of 100"^"* were as follows: 



,^ BCDEbFG 



^- Turpentine, 10-9 1405 187 19-6 232 32'75 



2. Turpentine, 215 234 293 368 38-3 43 6 55 9 

 3- Oil of lemon, 34 37'9 485 633 664 775 106 



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