1881.] Some Experiments on Metallic Reflexion. 489 







Quarter plate. 



Quarter plate. 







I. 





VI. 







P.I. 



P.A. 



P.I. 



P.A. 







o / 



o / 



o / 





Gold in carbon 



r Plate at A. 



76 10 



37 48 



71 37 



36 59 





Plate at B 



62 44 



37 40 



68 26 



36 43 



red liglit. 



I Mean value 



69 27 



37 44 



70 01 



36 51 



Gold in carbon 



r Plate at A. 



71 



39 09 



67 02 



37 17 



In *5nl"nVi in p « 



Plate at B. 



61 50 



38 24 



66 02 



37 10 



yellow liglit. 



L Mean value 



66 25 



38 46 



66 32 



37 13 



Grold in carbon i 



r Plate at A. 



59 51 



31 30 



54 24 



29 17 



bisulphide, •< 



Plate at B. 



61 30 



33 13 



67 56 



31 08 



blue light. 1 



. Mean value 



60 40 



32 21 



61 10 



30 12 



Corrected 

 numbers. 

 P.I. P.A. 



70 03 36 48 



66 32 37 12 



60 40 32 23 



The last column gives the values as corrected by Professor Stokes' 

 method (loc. cit., p. 248). 



The table shows, that for red and yellow light the observations 

 made with plate I, and for blue light those made with plate VI, are but 

 of little value ; whilst for red and yellow light the observations made 

 with plate VI, and for blue light those made with plate I, lie very 

 close to the corrected numbers. 



All subsequent experiments were therefore made with plate VI for 

 red and yellow light, and with plate I for blue light. 



The gold plate used in these experiments had been polished with 

 rouge, and from time to time rubbed with a little rouge, and then 

 with a clean chamois leather to remove the polishing powder. 



From some experiments with a silver plate, it appeared probable 

 that the optical constants of the plate might depend to a certain 

 extent on the nature of the polishing powder used, and therefore the 

 gold plate was dismounted and polished with putty powder, and then 

 well rubbed with a clean chamois leather, and the principal incidences 

 and azimuths determined. 



Four observations were determined in each position of the quarter 

 plate, two with the principal section of the polarising nicol on the 

 right, and two on the left of the plane of incidence; the plate VI being 

 used with red and yellow light, and plate I with blue light. 



Red light. Yellow light. Blue light. 



P.I. P.A. P.I. P.A. PI. P.A. 



("Plate at A. 75° 57 41 17 72 18 41 40 67 3^ 34 44 

 Gold plate m I plate ^ R n ^ M 2g n 21 4Q ^ QQ 34 g4 &5 



air ' LMean value 73 51 41 23 71 49 41 18 67 06 34 49 



After an interval of two months the measurements were repeated, 

 the plate being first rubbed with a clean chamois leather. 



