AND TRANSMITTED BY CERTAIN KINDS OF GLASS. 
285 
Percentage amount of Light Transmitted by Flint Glass. 
Repolishcd with putty and examined 
Original 
Not 
determinations. 
repolishcd. 
Immediately. 
After an interval. 
7 mm. thick . 
88-83 
92-66 
49 
85-40 
84-55 
85-03 
69-5 „ . . 
82-57 
84-^5 
91-3 „ . . 
80-74 
These numbers show that, except with the 24'3 mm. plate of crown glass, the effect 
of repolishing was to decrease the amount of light transmitted by both kinds of 
glass; they also show that, whilst the amount transmitted by the crown glass was the 
same as when it was first examined, the amount transmitted by the flint glass had 
increased considerably, although both kinds of glass had been kept during the interval 
wrapped in soft paper and in the same room. 
The 24'3 mm. plate of crown glass behaved difierently from the others. As is 
stated in Table XIII., it was first cleaned, and the amount of light it transmitted 
determined ; each surface was then polished for 20 minutes with fine rouge on a silk 
polisher. This produced no change, and the plate was, therefore, sent to an optician, 
who returned it with the statement that it had been “ polished with rouge on pitch, 
almost dry, to get a high polish.” The moment the glass was placed in the photo¬ 
meter the polish was seen to be defective, the surface being apparently grained, and, 
as the table shows, its transmissive power was greatly decreased ; it was returned to 
the optician to be again repolished, and then it let through more light than when 
first tested. 
The values of p, calculated with the value of a previously obtained (p. 280), are 
given in Table XXII. 
Table XXII. 
Values of p for the Crown Glass. 
Original 
Not 
Repoli.shed with 
Repolished with 
determinations. 
repolished. 
rouge. 
putty. 
6-5 mm. plate . 
-9648 
•9650 
•9601 
II-5 „ . . 
•9636 
•9647 
•9617 
■9619 
15-0 „ . . 
•9629 
•9640 
•9601 
•9608 
18-5 „ . . 
•9648 
•9644 
v_ ^ ^ 
24-3 „ . . 
•9642 
•9642 
[-9672] 
Mean .... 
•9641 
•9645 
•9609 
