488 



Sir J. Conroy*. 



[Mar. 3, 



The same gold plate which had been used in the previously de- 

 scribed experiments was fastened to the stage of the goniometer, and 

 the principal incidences and azimuths observed with yellow and bine 

 light, when the plate was in air, water, and carbon bisulphide. 



An alcohol flame with a salted wick and a paraffine lamp, with a 

 glass trough filled with ammonio-sulphate of copper placed in front 

 of it, were used as the sources of light. The light transmitted by the 

 deep red glass used in the previous experiments and by the ammonio- 

 sulphate was not homogeneous. 



The light of the greatest intensity in the one case was slightly more 

 refrangible than C, and in the other of a refrangibility nearly midway 

 between F and Gr. 



The polarising nicol was placed with its principal section at an 

 angle of 45° with the plane of incidence in each of the four quadrants 

 successively, and two observations made with the nicol in each posi- 

 tion ; so that the value of the principal incidence and the principal 

 azimuth for each position of the " quarter undulation plate " is the 

 mean of eight observations. 



The following table contains the results of these experiments ; the 

 values for red light, which had been previously obtained, are included 

 in it for the sake of comparison : — 



Corrected 

 numbers. 

 P.I. P.A. 



Gold in air, 

 red light. 



Plate at A. 



Quarter plate. 



Quarter plate. 



I. 





VI. 



P.I. 



P.A. 



P.I. 



P.A. 











80 13 



35 52 



78 03 



35 43 



70 45 



35 57 



73 45 



35 21 



75 29 



35 54 



75 54 



35 32 



76 33 



38 12 



73 59 



36 27 



63 33 



37 39 



72 55 



36 20 



72 33 



37 55 



73 27 



36 23 



65 32 



30 19 



60 27 



32 31 



69 03 



29 44 



71 51 



32 09 



67 17 



30 01 



66 09 



32 20 



•6 35 27 



™ , , . . r Plate at A. 

 Gold in air, 



n t i i. -s Plate at J3. 

 yellow light. 



J ° L Mean value 72 33 37 55 73 27 36 23 73 28 36 22 



Gold m air, J Plate at B. 



blue light. [ M ean value 67 17 30 01 66 09 32 20 67 24 29 47 



red light. 



Gold in water, 

 yellow light. 



Gold in water, 

 blue light. 



Plate at A. 



76 46 



37 13 



74 46 



36 







Plate at B. 



66 46 



35 50 



70 25 



36 49 







Mean value 



71 46 



36 31 



72 35 



36 24 



72 46 



36 23 



Plate at A. 



73 47 



38 05 



70 05 



37 28 







Plate at B. 



65 29 



38 27 



68 51 



36 22 







Mean value 



69 38 



38 16 



69 28 



36 55 



69 28 



36 52 



Plate at A. 



61 51 



28 30 



57 09 



31 35 







Plate at B. 



65 26 



29 06 



70 59 



31 01 







Mean value 



63 38 



28 48 



64 04 



31 18 



63 36 



28 38 



