MR B. STEWART ON RADIANT HEAT—SECOND SERIES. 69 
TABLE V. 




Proportional Radiation of Glass Plates at different Temperatures (Radiation of Lamp-black= 100). 
Thickness of Plate.| 5 emP hae Beene oe 390° C. | 100° ©. 
mm 
0:07 16 37 61 | 84 
| 5 40 | 58 84 95 
1-0 48 64 87 96 
| 2 53 70 89 96 
4 | 58 | 75 | 91 96 
6 60 | 77 92 96 | 
8 61°5 78 92°6 | 96 MM EE eles ae ue sacl 




38. Let us call the proportional radiation of a glass plate at 100° C. unity, 
and we derive the following table. 
TABLE VI. 

Proportional Radiation of Glass Plates at different Temperatures, their respective Proportional 
Radiations at 100° C. being reckoned Unity. 


Thickness of Plate. 100° ¢, 390° © Yee Ae oe ae eae ere 
mm . 
0-07 is 72 ‘44 19 
19) HH 88 ‘61 42 
1:0 1 “91 66 “50 
2 1 93 ‘73 05 
4 1 ‘95 ‘78 60 
6 iL ‘96 80 -62 
8 1 *965 ‘81 ‘64 




39. We see thus that the radiation of thick plates of glass increases most 
rapidly, and that of thin plates least rapidly, as the temperature increases, and 
we may suppose, that if we could procure a plate of glass of sufficient tenuity, we 
might (without heating the plate at all), by finding its absorption for heats of 
different temperatures, find its radiation at those temperatures, which (if the 
plate were thin enough) would give us the law of radiation of a glass particle. 
This law would not increase nearly so fast with increasing temperatures as 
