490 



Sir J. Conroy. 



[Mar. 3; 



Red light. Yellow light. Blue light. 



P.L P.A. P.I. P.A. P.I. P.A. 



r Plate at A. 76 20 42 40 7°2 16 41 07 6°7 59 37 12 



Gold plate in J Plate at B 7l 49 42 5 70 59 41 14 66 29 35 50 



air - I Mean value 74 04 42 22 71 38 41 10 67 14 36 31 



The measurements were then made with the plate in water and 

 carbon bisulphide. 



Gold plate in f 

 water. I. 1 



Gold plate in 

 water. II. 



Gold plate in 

 carbon 

 bisulphide. 



The mean values of these two series of determinations are — 





Red light. 



Yellow 



light. 



Blue light. 





P.I. 



P.A. 



P.I. 



P.A. 



P.I. 



P.A. 





o / 













Plate at A. 



72 43 



42 36 



69 23 



42 10 



63 50 



36 44 



Plate at B. 



63 07 



42 39 



67 28 



41 01 



62 39 



35 12 



Mean value 



70 25 



42 37 



68 25 



41 35 



63 14 



35 58 



Plate at A. 



73 17 



42 10 



67 11 



39 25 



64 27 



36 07 



Plate at B. 



68 18 



42 24 



66 36 



42 25 



62 25 



36 41 



Mean value 



70 24 



42 17 



66 53 



40 55 



63 26 



36 24 



Plate at A. 



71 52 



42 37 



66 58 



41 26 



61 41 



36 19 



Plate at B. 



66 57 



42 29 



66 14 



41 56 



58 29 



37 35 



Mean value 



69 24 



42 33 



66 36 



41 41 



60 05 



36 57 



Gold in air 



Bed light. 



YeUow light. 



Blue light. 



P.I. P.A. 



P.I. 



PA. 



P.I. P.A. 





/ 







7°3 57 41 52 



71 43 



4°1 14 



67 10 35 40 



70 24 42 27 



67 39 



41 15 



63 20 36 11 



69 24 42 33 



66 36 



41 41 



60 05 36 57 



The values of the principal azimuths are considerably higher 

 (about 6°) than those previously observed ; and in the case of red and 

 yellow light, when the gold plate was in air or water the principal 

 incidences are lower (about 2°) than with the plate polished with 

 rouge ; but with blue light, and also when the plate was in contact 

 with carbon bisulphide, there was but little difference in the values 

 of the principal incidences. 



The plate was again cleaned with rouge, and the measurements in 

 air repeated. 







Red light. 



Yellow 



light. 



Blue light. 







P.I. 



P.A. 



P.I. 



P.A. 



P.I. 



P.A. 











o / 



o / 



o / 



o / 





r Plate at A. 



76 41 



41 07 











Gold in air. j 



Plate at B. 



72 05 



41 16 













- Mean value 



74 26 



41 11 













' Plate at A. 



76 31 



40 47 



72 46 



40 39 



69 07 



34 44 



Gold in air. j 



Plate at B. 



72 11 



40 15 



72 06 



39 40 



67 55 



33 05 





- Mean value 



74 21 



40 31 



72 26 



40 09 



68 31 



33 51 



