1883.] Some Experiments on Metallic Reflection. 



35 



case with the other three mirrors. All four mirrors had appeared 

 perfectly untarnished and bright when the observations were made, 

 but as the silver, steel, and tin mirrors had been polished some months 

 before they were used, it was thought possible that slight films might 

 have formed on their surfaces, and that the difference in the calculated 

 and observed results was due to this cause. The silver mirror was 

 therefore returned to the maker, Mr. Hilger, to be repolished with 

 putty power. 



The amount of light reflected by it was determined the same day 

 that it was received back, and it was found that its reflective power 

 was slightly diminished for light incident upon its surface at angles 

 of 20°, 40°, and 60°, and somewhat increased for light incident at 

 80°, the number being — 



20° 68 '54 



40 69-01 



60 72 -65 



80 85 -96 



These results agreeing fairly well with the means of the numerous 

 observations which had previously been made, it was not thought 

 necessary to make any further determinations, as it was clear that the 

 difference between the observed and calculated values could not be due 

 to a film on the surface of the mirror. 



The surface of the silver mirror not being very good, it was again 

 returned to the maker to be polished with rouge, that being stated to 

 be the best material for polishing silver; the result was not very 

 satisfactory, as the surface appeared less good than before — that this 

 was really the case was confirmed by the reflective power of the 

 mirror being diminished. 



The results of three series of observations are recorded in table, 

 and also two determinations of the values of the principal incidences 

 and azimuths. 



Angle of 

 Incidence. 



A. 



B. 



C. 



Mean Value. 



o 



10 



58-69 



63-01 



61 -38 



61-03 



20 



61 -02 



63 -95 



63-74 



62-90 



30 



62 -48 



64-80 



66 -21 



64 -49 



40 



64-27 



66-57 



66 -95 



65 -93 



50 



65 -24 



67 -82 



68-50 



67 19 



55 



65 71 



68-19 



69 -89 



67-93 



60 



66-71 



70-19 



70-98 



69-29 



65 



68 -88 



70-54 



70-11 



69 -84 



70 



68-95 



72-77 



72-71 



71 '48 



75 



70-87 



73 -43 



77 '26 



73 -85 



80 



77-16 



78 -92 



83-15 



79 -74 



D 2 



