284 
SIR J. CONROY ON THE AMOUNT OF LIGHT REFLECTED 
More observations were made with the glass before repolishing than after, which 
accounts for the one curve being so much smoother than the other. 
These results show (1) that repolishing increased the amount of the reflected light; 
(2) that before repolishing the amount of light reflected was less than the theoretical 
amount calculated from the observed index of refraction of the glass, but that in the 
case of the crown glass, by assuming a value for the index in accordance with the 
amount of light reflected at a perpendicular incidence, the amount reflected at other 
angles by the glass before repolishing was given correctly by the formula ; (3) that 
after repolishing the observed amount of light reflected exceeded the calculated 
amount; (4) that in the case of the flint glass what may be described as the 
“ polishing-eflect ” passed off in the course of a day or two, and then the theoretical 
and actual intensities of the reflected light agreed, but that with the crown glass this 
did not appear to be the case. 
The effect of repolishing being to increase the amount of light reflected by the glass, 
it seemed desirable to ascertain whether repolishing would produce any change, and, 
if so, whether increase or diminution, in the amount transmitted. If the increase in 
the reflected light were due to a more perfect surface being obtained, and, therefore, 
to less light being irregularly reflected or diffused, the intensity of the transmitted 
beam would certainly not be weakened by repolishing ; if, however, it were due to an 
increase in the refractive index of the surface-layer of the glass, then the mtensity of 
the transmitted beam would be decreased. 
Table XXL contains the means of the values set forth in Tables XIII. and XIV., 
and in the second column the values for tlie transmitted light obtained with the same 
samples of glass two years previously (see Table VI.). 
Table XXI. 
Percentage amount of Light Transmitted by Crown Glass. 
Original 
Not 
Repolislied with 
Repolished with 
determinations. 
repoli.sLed. 
rouge. 
putty. 
6'5 mm. 2 ;)late . 
91-.50 
91-53 
90-60 
11-5 „ . . 
90-07 
90-28 
89-77 
89-75 
15-0 
89-13 
89-31 
88-61 
88-72 
18-5 ,, . . 
88-51 
88-55 
24-3 „ . . 
87-16 
8G-91 
87-77 
