C46 DE. E. FEANKLAND ON THE INFLUENCE OF ATMOSPHEEIC PEESSUEE 
This series was continued down to 4’6 inches pressure, but the illuminating power of 
the flame could then no longer be measured by the photometer. 
/3. Influence of Comjpression. 
The foregoing experiments having demonstrated a very remarkable diminution 
of light in candle- and gas-flames by a reduction of atmospheric pressure, it became 
interesting to ascertain the effect of compressed air upon the luminosity of similar 
flames. At the very outset of this part of the inquiry considerable difficulties presented 
themselves, since it became necessary to abandon a gaseous combustible, which could 
not be compressed to the necessary degree, and then delivered at a uniform pressm’e 
through a burner, without very complex apparatus. I was thus compelled to resort to 
solid or liquid combustibles, the irregularities of which were still further increased by 
the space within the combustion-chamber being necessarily more confined, in order that 
its walls might the better sustain high pressures. These difliculties in the way of accm’ate 
determinations were, however, by no means the most formidable ; for it was soon found 
that any considerable increase of atmospheric pressure caused both candle- and oil-flames 
to throw ofi" large quantities of fuliginous matter, the formation of which could not be 
prevented by any amount of draught that could be established in the chimney of the 
apparatus. Hence, although the luminosity of the flames was greatly increased, yet it 
was obviously much less so than would have been the case under conditions of more 
perfect combustion. In fact it soon became evident that the determinations of increase 
of luminosity by compression must be made in a manner precisely the reverse of that 
employed for the corresponding determinations in rarefied air ; for whilst in the latter 
case the experiments were made with flames, which at ordinary atmospheric pressure 
were saturated -with carbon particles, in the former it was found necessary to commence 
with flames which were very feebly, or not at all luminous at common pressures. Such 
is the effect of compressed air in determining the precipitation of carbon particles 
within the flame, that a small alcohol lamp, which at the ordinary pressm’e burnt with 
a pure blue flame, became highly luminous when placed under a pressure of four atmo- 
spheres ; and it can scarcely be doubted that at a pressure of five or six atmospheres, its 
luminosity would be equal to that of sperm oil burning at atmospheric pressure. 
The apparatus employed, and which is shown in Plate XVIII. fig. 2, was very similar 
to that used in the previous part of the inquiry. A is the gas-governor regulating the 
supply to the standard flame B. H H is the photometer arranged as before, and a a are 
the ground plates, rods, and screws for securely closing the ends of the glass cylinder 
containing the experimental flame. The comparatively thin and wide cylinder used in 
the rarefaction experiments was here replaced by the strong glass cylinder D, 12 inches 
long, 2 inches internal diameter, and inch thick ; e is the lamp furnishing the ex- 
perimental flame ; it is fixed upon the rod I passing through a stuffing-box in the lower 
plate, and enabling it to be adjusted to any height, b and c are the glass chimney 
and stopcock arranged as before, except that c now opens at once into the air. The 
