638 DE. E. EEANKLAND ON THE INELHENCE OF ATMOSPHEEIC PEESSHEE 
from currents of air by a cylindrical glass shade. The vessel or receiver, in "which the 
experimental flame was made to burn under diflerent atmospheric pressures, consisted 
of a glass cylinder 12 inches high and 4^ inches in diameter, welted and ground at 
both ends, which could be closed air-tight by the ground cast-iron plates a a, between 
which and the ends of the cylinder collars of leather were introduced, so as to distribute 
more evenly the pressure exerted by the nuts and screws of the three steel rods binding 
together the upper and lower plates. 5 is a glass chimney contracted at top and ce- 
mented with plaster of Paris into the stopcock c, which opens the communication for the 
exit of the products of combustion ; is a similar stopcock inserted into the under plate, 
for the admission of air into the cylinder. The gas-delivery tube e passes air-tight 
through a stuffing-box yin the cover of the cylinder, and was most carefully united with 
the exit-tube of the meter so as to exclude the admission of any trace of air during the 
experiments, and especially Avhilst the gas was being consumed under reduced pressure. 
The atmosphere within the glass cylinder D could be uniformly maintained at any 
pressiue, from that of the atmosphere downwards, by means of the air-pump E and the 
reservoir E. The latter was constructed of wrought iron, and, having a capacity of 2-| 
cubic feet, served to maintain a very constant pressure unaffected by the intermittent 
action of the air-pump. The pressure in the reservoir, and consequently in the glass 
cylinder D, was indicated by the gauge G, which was usually worked with mercury, but 
occasionally, as described below, with Avater. H H is a Bunsen’s photometer, by means 
of Avhich, the relative intensity of the light of the standard flame and of the experimental 
flame Avas determined. The moveable paper disc g was protected from diffused light by 
the cylmder Ji A, so placed that the line joining the two flames passed through its axis. 
This cylinder was pierced with two apertures at opposite sides, — the one in front (shoAAm 
in the figiu’es) allowing the observer simultaneously to see the reflected images of both 
sides of the disc in tAvo mirrors (not shown in the figure) placed at a proper angle behind 
the opposite aperture. 
Such is a general outline of the arrangement of the apparatus used ; but the following 
additional particulars may serve to illustrate more fully the mode of Avorking, and also 
to explain some of the details of the figure not yet alluded to. The test-meter C was 
constructed in the usual manner, so as to show by observations of one minute’s duration, 
the rate of consumption per hour ; but, in order to ensure greater accuracy, these obser- 
A'ations Avere always extended over a space of at least five minutes, and were repeated 
at intervals during the course of the determinations at each particular pressure. In 
order to have the rate of admission of gas to the experimental flame perfectly under 
control, a micrometer stopcock (^) was inserted in the exit-tube of the meter. Just above 
the internal orifice of the stopcock d, was placed a circular disc, so as to prevent the 
current of air from impinging upon the experimental flame ; by this arrangement the 
latter alAA^ays burnt with perfect steadiness. It is well known that the illuminating 
effect of a gas-flame depends very considerably upon the velocity of the current of air 
in which it burns, and that the maximum illuminating effect is always produced when 
