Gas-Burners , and on the Illuminating Power of ' the Gases. 5 
This has been denied by several of its defenders. Mr Buchanan, civil-engi- 
neer in this city, has denied it in a report published not long ago by the Coal-Gas 
Company ; and more lately his statements have been confirmed by Mr Ritchie 
of Tain (Edin. Journ. of Science , v. ii. p. 323.) ; yet we repeat, that frequent trials 
leave us no room to doubt, that non-luminous heat does affect it. A low tem- 
perature, indeed, will not affect it ; and we must acknowledge, " that some error 
had crept into those experiments which formerly led us to believe that it was 
influenced even by the heat of boiling water. For we have since found, that 
the instrument remains stationary, not only before a vessel of boiling water, 
but likewise when placed five inches from a gas-burner, which was covered 
with a rough copper chimney, and radiated heat enough to raise a small mer- 
curial thermometer, at the same distance, five degrees of Fahrenheit. But 
when the heat is more intense, it is decidedly acted on. Thus, at the dis- 
tance of 74 inches from an iron cylinder 7 inches by 2, heated short of be- 
ing luminous in the dark, and held perpendicularly, it fell 24 degrees, being 
half a degree more than when placed at the same distance from the flame of a 
good Argand oil-lamp. A small mercurial thermometer rose 14 degrees at the 
distance of 74 inches from the cylinder. 
Lest any error might arise from an accidental obliquity of position, which 
it is very difficult to prevent when the hot body has a large surface, and is so 
near the instrument, we repeated the experiment in the following manner. 
A tolerably steady source of non-luminous heat was procured, by placing 
it before a chamber fire well packed, burning clear without flame, and com- 
pletely skreened by a conical sheet-iron baquet, resting with its open end on 
the ribs. The photometer being placed 3 inches from the bottom of the 
baquet, and nearly parallel to its surface, fell 44 degrees ; and when turned 
on its centre, till the position of the balls was exactly transposed, it fell 154 de- 
grees. The mean of these observation is 1 0 degrees, which is the true effect 
of the heat, when allowance is made for its unequal action on the two balls. 
The heat in the place occupied by the photometer was pretty steadily 50° 
Fahrenheit above that of the room. 
This experiment was ^.repeated before a Black’s furnace, which had been 
kindled for some time, and gave out heat enough to raise the thermometer, at 
the distance of 4 inches, 50 or 55 degrees above the temperature of the apart- 
ment. In the first trial, the photometer indicated, at the distance of 4 inches, 
— > 1° in one position, and + 22°.5 when turned half round, shewing the diffi- 
culty of placing it so as to expose it equably to so large a surface. When 
its original position was altered a little, it fell 5 degrees, the thermometer 
standing 514 degrees above the temperature of the room; and when turned 
half round, it fell 16 degrees, the thermometer standing 4 degrees higher than 
before. The mean is 104 degrees, which corresponds nearly with the former 
experiment, made at almost the same temperature. 
So much for the effect of non-luminous heat on the Thermometric Photo- 
meter. 
But, secondly , it is acted on by lights of different colours in a way that bears 
no relation whatever to their illuminating power. For reasons formerly assigned, 
we shall not at present discuss this subject at large. It appears that lights of a 
red colour, compared with white lights, have a heating power superior to their 
