1 879.] The Temperature of the Sun . 733 
an equal quantity of gas per minute, was the same whether 
the jets were arranged with all their surfaces presented to 
the screen, or with the surface of only one presented, the 
others being ranged behind that one and at equal mean dis- 
tance to the larger surface ; or, in other words, that thick- 
ness or depth of flame is a facftor of equal value to that of 
surface area. The flame itself was found to be transparent, 
but the products of its combustion not so. The diather- 
mancy of flames was similarly tested, but with inferior 
apparatus. The results showed that every additional flame 
placed behind others increased the thermal radiations from 
a given restricted area facing the thermometer ; but the 
increase was not so strictly proportionate to the quantity of 
gas consumed as in the case of the luminous radiations. 
The variations, however, were not greater than the limits of 
error due to the rude experimental appliances. 
Further investigations are demanded for reliable quanti- 
tative determination of the amount of thermal radiations 
which will pass through a flame or flames of given thick- 
nesses. My experiments indicate (though not sufficiently 
delicate to prove) that a flame offers no resistance at all to 
the passage of the thermal radiations from a flame similar 
to itself; and if I am right, the vast energy of the solar 
rays demand no preter-terrestrial intensity of temperature in 
the sun, but merely a great quantity of heat, due to a great 
depth of flame of no higher temperature than is produced 
here on earth by the re-combination on the photosphere of 
those elements which we are justified in regarding as disso- 
ciated in the interior or lower regions of the solar envelope, 
and re-combining in the photosphere. 
As Prof. Langley is familiar with the phenomena of the 
Bessemer process, I will direCf his attention to a magnificent 
illustration of the effeCt of body or thickness of flame which 
it affords. Every chemist knows how feeble is the luminosity 
of the blue flame which accompanies the combustion of 
carbonic oxide. When the spiegeleisen is poured into the 
Bessemer converter some of the carbon of the spiegel com- 
bines with the oxygen of the fused oxide of the blown iron, 
and a huge blue flame of unmistakable character emerges 
from the mouth of the converter. Its intrinsic luminosity 
is visibly small, comparable to that of the flame we produce 
in the ledfture experiment of decomposing oxalic acid in a 
test-tube, and lightingthe carbonic acid at the tube's mouth. 
The radiant energy of this body of pale flame (which has 
no hollow centre like common flames receiving their oxygen 
from the outside atmosphere) is nevertheless wonderfully 
3 a z 
