268 
&IR J. CONROY ON THE AMOUNT OF LIOHT REFLECTED 
Section III.—Amount of Light Refected at a nearly Perpendicalar Incidence 
after Repolishmg. 
Lord Kayletgh found (‘E,oy. Soc. Proc./ vol. 41, p. 389) that, although the glass 
surfaces he examined were free from any apparent tarnish, the amount of light they 
reflected was largely increased by repoiishing. The wedge of crown glass was, there¬ 
fore, repolished on December 21, 1887, by means of a disk of wood charged with 
putty powder and mounted in a lathe (the same method that Lord Rayleigh had 
used), and its reflective power redetermined immediately; it was found to reflect 
4’29, instead of 378, per cent. The glass was again examined on January 5, 1888, 
and it then reflected 4'20 per cent. 
Two days later the glass was repolished a second time with fine rouge, and again 
examined ; it reflected 4‘22 per cent, of the incident light. 
After an interval of five months, on June 13, this piece of glass, the surface of 
which had become considerably tarnished, was rubbed with wash-leather until the 
moisture deposited on the glass by breathing gently on it evaporated quite uniformly ; 
it was then examined, and found to reflect 4‘42 per cent, of the incident light. 
The next day it was repolished for the third time, and examined immediately ; it 
reflected 4‘30 per cent. 
An attempt was made to repolish the flint glass w'edge on February 28, 1888, with 
both putty and rouge, but a surface free from scratches could not be obtained. Its 
reflective power, however, was increased, and it reflected 6'20 per cent., instead of 
5'20, after this imperfect polishing. 
The surface not being satisfactory, the glass was sent to Mr. Hilger to be 
repolished. It was received back on the evening of March 2, and examined on the 
3rd ; it reflected 6'06 per cent. 
After three months the glass was again examined, the film which had formed on its 
surface having been previously removed by rubbing with a wash-leather ; it only 
reflected 571 per cent., although the surface appeared perfectly polished. On 
June 11 it was repolished with very fine washed rouge, and w^as found to reflect 
6’25 per cent, of the incident light. Two days later, on June 13, it only reflected 
573 per cent. 
The polishing with putty powder was effected by means of a soft wood disk, 
mounted in a lathe, the disk being kept moist. For the rouge a polisher w'as formed 
by cementing a piece of silk to a sheet of plate glass fastened to a table, and charging 
this with carefully waslied rouge : the glass was held against the rapidly rotating 
disk in the one case, and rubbed over the fixed surface in the other. The relative 
velocities of glass and polisher were very different in the two cases, and wdth the disk 
the friction was sufficiently great for the glass to become sensibly w^arm. 
