32 Experiments an the Relative Intensities 



The mean of these five experiments gives for the 

 loss of light .3494 ; and from hence it appears that 

 more than \ part of the light which falls upon the best 

 glass mirror that can be constructed is lost in reflec- 

 tion. 



The loss with mirrors of indifferent quality is still 

 more considerable. With a very bad common looking- 

 glass the loss, in one experiment, appeared to be .4816 

 parts; and with another looking-glass it was .4548 

 parts in one experiment, and .4430 in another. I 

 should certainly have made an experiment to deter- 

 mine the loss of light in its reflection from the surface 

 of a plane metallic mirror, but I had no such mirror at 

 hand. 



The difference of the angles of incidence at the 

 surface of the mirror, within the limits mentioned, 

 namely, from 45 to 85, did not appear to affect in 

 any sensible degree the results of the experiments. I 

 also found upon trial that the effect produced by the 

 difference of the angles at which light impinges against 

 a sheet of transparent glass through which it passes is, 

 within the limits of 40 or 50 from the perpendicular, 

 but very trifling. 



