32 Experiments on 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. 



