146 Mr. Dyke on the Determination of the Mean Spherical 



CP. = mean of C.P.'s in positions in which axis of 

 loops of filament is parallel to photometric 

 bench. 



M.H.C.P. = mean horizontal candle-power. 



M.S.C.P. = mean spherical candle-power. 



Lamp 



No. 



C.P. 



M.H.C.P. 



M.S.C.P. 



Reduction Factors. 



M.H.C.P. 

 C.P. 



M.S.C.P. 

 C.P. 



M.S.C.P. 

 M.H.C.P. 



1 



16-6 

 16-6 

 16-4 

 15-9 

 16-0 

 16-0 

 8-0 

 30-5 

 31-8 



16-1 

 16-0 

 162 

 14-8 

 14-9 

 15-1 

 7'5 

 293 

 299 



12-5 

 12-8 

 130 

 125 

 11-7 

 12-2 

 6-2 

 24-5 

 24-2 



•97 

 •97 

 •99 

 •93 

 •94 

 •94 

 •93 

 •96 

 ■94 



•75 



•77 

 •79 

 •79 

 •73 



•76 



•77 

 •80 

 •76 



•78 

 •80 

 •80 



•85 

 •78 

 •81 

 •83 

 •84 



• 81 



2 



3 



4 



k :::::: 



< 



It is obvious, however, that these reduction factors are of 

 very little use unless they remain sensibly constant for 

 different lamps of the same type of filament. 



The following table shows the reduction factors for seven 

 lamps of type 5 : — 



Lamp No. 



Reduction Factors. 



M.H.C.P. 

 C.P. 



M.S.C.P. 

 C.P. 



M.S.C.P. 

 M.H.C.P. 



5, 



•94 

 •92 

 •92 

 •96 

 •93 

 •95 

 1-00 



•73 

 •71 

 •72 

 •74 

 •72 

 •74 

 •79 





78 

 78 

 78 

 78 

 78 

 78 

 79 



si . 



5 B 



k ::::::::::::::: 



5* 



5 " 



fc 



^H 







This table shows clearly that only one reduction factor is 



M S C P 

 of practical utility, namely, the ratio iyr tt p p • 



This one factor, however, is remarkably constant and 



appears to be very little altered by a distorted filament ; 

 thus, although in 5h the filament was so much bent as to 



