TRANSACTIONS OF SECTION A. 427 
be untrustworthy as a standard of light, and recommended the employment 
in their stead of the air-gas flame. At present the Board of Trade have taken 
no action upon this Report, and the quality of the gas which the companies 
are to supply remains in the hands of the candle-makers. The lamp now 
placed betore the Section, and represented by the above figure, is the result 
of an attempt to bring the air-gas standard into favour by giving it a simple and 
ortable form. The burner and the flame are identical with those to which reference 
fas been made. But to form the standard gas, instead of 3 cubic feet of air 
mixing in a holder with 1:05 cubic foot of vapour formed from 9 cubic inches 
of standard petroleum, or pentane, the air and vapour mix in a small reservoir, and 
thence flow down to the burner. At one point the diameter of the pipe through 
which they flow is reduced, and this reduction and the height of the reservoir are 
so related that when a mixture in the above-named proportions is entering the pipe 
it burns with a flame of the standard height of 24 inches. In constructing the 
lamp the aperture in the tube or height of the reservoir was varied until the light 
given by the lamp was exactly equal to that given by the standard flame obtained 
from air-gas made up in the holder. With a lamp thus constructed the height of 
the flame depends upon the proportion in which air and the heavy vapour are 
mixed. If there is more air the density of the mixture and the consequent flow 
are reduced; and also the poorer gas burns with a shorter flame. If there is more 
pentane vapour the density of the mixture and the consequent flow are increased ; 
and also the richer gas burns with a longer flame. Thus to each height of flame 
belongs, for the same lamp, a particular mixture of air and vapour. This lamp has 
been so made that the standard mixture produces—and no other mixture can 
produce—the standard height of flame. The flame of the lamp is therefore iden- 
tical with the pentane flame which has been tested and used hitherto. And, as 
the construction of the lamp involves no small measurements, other lamps can 
readily be made which, fed with the same liquid and adjusted to give a 23-inch 
flame, will give the same light as this lamp. 
The means by which the height of the flame may be adjusted will be understood 
from the figure. By the turning of a screw water is forced into the reservoir, and 
the surface of the pentane which floats upon the water is raised nearer the mouth 
of the pipe down which the air-gas flows. The proportion of pentane vapour is thus 
increased ; it is diminished by lowering the level. A supply of pentane approxi- 
mately equal to the consumption is furnished from a bulb and stopeock which 
delivers a drop about once in five seconds; and a supply of heat is brought by a 
rod and disc extending above the flame at a distance and inclination which must be 
varied according to the temperature of the room in which the lamp is used. It is 
only necessary that the supply of heat should not be so small as to require the 
raising of the pentane to the top of the pipe, nor so large as to give a high flame 
when the surface of the liquid is at a low level. None of the adjustments named 
has been found difficult in practice. 
12. On some Results of Photographing the Solar Corona without an Helipse. 
By Wiuuiam Hveerns, D.C.L., LL.D., F.R.S.—See Reports, p. 346. 
13. On the Internal Constitution of the Sun. 
By Professor ArrHur Scuusrer, F.2.8. 
The idea that the sun is a gaseous body is gradually gaining ground. It could 
not be otherwise, for the interior of the sun cannot be permanently at a lower 
temperature than the surface, which we know to be sufficiently hot to yolatilise 
some highly refractory metals. 
Tf the sun is a gaseous mass it must be in convective equilibrium, and the 
distribution of temperature within it must be determined by the adiabatic law. 
Only thus could its small density be explained. 
