596 PROCEEDINGS OF THE AMERICAN ACADEMY. 



0.46 per cent. On this account the energy E of the standard radiation 

 must be reduced by the above percentages. Applying these corrections * 

 and the corrections due to the diffused radiation from the black coating 

 on the silver disc, the energy of the standard radiation becomes 



/ X t, 1 • rr 0.986 



(a) through air, E^ X ^-^^ ; 



{b) through red glass, E^ X ^^^ ; 



/ ^ u r. t:. 0.995 



(c) through water, E^ X ^-^ . ^ 



Hence the pressure produced by standard radiation calculated by Max- 



well's formula, p = -z — ^ , since p = 0.848, becomes 



o X lU 



/ N u r. . 7.^ 1-848 0.986 



(a) through air =Ax ^-^—^, X ^^^ 



1.848 0.986 ,^„ , 

 = (7.05 ± 0.03) X 10-^ dynes ; 



/.x ,_ 1, J , r» 1-848 0.986 



(b) through red glass = E^ X ^ ^ ^^,, X ^^^ 



1.848 0.986 ,^„ , 



= ^-'''^^^OO^o^O:954><^^^y"^^ 



= (6.86 ± 0.03) X 10-^ dynes ; 



, N , , rr 1-848 0.995 



(c) through water = E^ X ^^^^^ X ^^^ 



1.848 0.995 



- ^-^^^ ^ ^^TiFo ^ 0:954 ^ ^^^^^^^ 



= (6.48 ± 0.04) X 10-^ dynes. 



* As the average pitch of the cone of the incident beam was about one part in 

 forty, no correction need be applied for inclination. Furthermore, the inside of 

 the bell-jar was blackened and the zero of the balance was so chosen that energy 

 reflected from the window admitting the beam could produce no pressure effects. 



