the passage of radiant heat through glass screens . 375 
shall content myself with giving a few of the most decisive, 
in a tabular form. 
The first experiments I shall give, are two sets made with 
only one reflector, in the focus of which the bulb of a large 
differential thermometer was placed, and the progress of the 
effect traced for every 30 seconds successively in the three 
cases. The area of heating rays was limited by a circular 
aperture, about two inches diameter, in a pasteboard screen. 
The first screen, or that nearest the ball, was about ~ inch 
in thickness, the second rather less. The divisions on the 
scale are arbitrary. 
One Reflector. Dist. 18 inches. 
No. I. 
Min. 
Sec. 
No Screen. 
1 Screen. 
2 Screens. 
O 
O 
O 
O 
3° 
s 
°-5 
O 
1 
— 
9 
1 
O.25 
3° 
12 
1.25 
0.25 
z 
— 
*3-5 
1.25 
0.25 
30 
14-S 
*•5 
O.25 
3 
— 
J 5 
*•5 
O.25 
30 
*5-5 
*•75 
°5 
4 
— 
l 5-75 
*•75 
0.25 
30 
16 
*•75 
0.5 
5 
— 
I 575 
*•75 
o-5 
3° 
>5-5 
*•75 
°>5 
6 
— 
*5 
*•75 
0.25 
30 
*•5 
0.5 
• 
* 
• 
* 
8 
30 
*•5 
* 
9 
— - 
1.25 
# 
11 
0.25 
One Reflector. Dist. 18 inches. 
No. II. 
Min. 
Sec. 
No Screen. 
1 Screen. 
2 Screens. 
O 
0 
O 
0 
3 ° 
s 
I 
0.5 
I 
— 
9-5 
*•5 
I 
3 ° 
13 
2 
I 
2 
— 
>5 
2 
I 
30 
16 
2.25 
I 
3 
— 
16 
2.5 
I 
3 ° 
> 6.75 
2.5 
I 
4 
— 
16 
2.25 
I.25 
30 
> 5-75 
2.25 
I.2S 
S 
— . 
* 5-5 
2 
I.25 
3 ° 
>5 
2 
1.5 
6 
— 
* 4-75 
2 
*•5 
* 
* 
* 
8 
3 ° 
*•5 
9 
— 
I.2§ 
u 
— 
1.25 
30 
I 
(6.) In these experiments it appears that the effect with two 
screens is in a much greater ratio to that with one, than this 
to the direct effect. It is also obvious on inspection, that the 
