On the Invisibility of certain Colours to certain Eyes. 158 
that if, when the flame was in this last state, the vessel-of the 
gas was inverted, the flame was instantly changed ; and instead 
of being as I have just stated, it was steady, silent, and power- 
ful. I have repeated the experiment frequently, and with dif- 
ferent vessels. In every instance the result has been precisely 
the same. ! 
It became interesting to inquire into the cause of the phz- 
nomenon. . I submit with deference the only explanation which 
I have been able to discover. : 
The gas, rarefied by heat, being lighter than the atmosphere, 
has a tendency to move in the direction of the flame when the 
vessel is held upright. In this case, therefore, it moves with 
greater impetuosity than it could were the burner in any other 
position. On the contrary, when the flame is directed down- 
wards, it has a tendency to return upon itself. ‘Thus the ascent 
of the gas is promoted, and the descent retarded, by the agency 
of the atmosphere; for the gas being rendered lighter in the 
way just mentioned, has a tendency to rise in the air on the 
same principle that a cork rises in water, and its descent is in 
like manner resisted. The fact might, perhaps, be better illus- 
trated by conceiving air to be forced through water. If the 
air be urged from the bottom of the vessel, it readily moves by 
reason of its great levity in the required direction ; but if it be 
forcibly impelled downwards from the. surface, as from the 
extremity of a condensing syringe, it can only be driven to a 
short distance, and it is then forced back towards the pipe. 
This case appears to me to be analogous to that of the gas, 
which, if I am not mistaken, it serves to illustrate and explain. 
The upright position of the vessel admits, in the case referred 
to, of the escape of some of the gas unburnt; but when the 
burner is inverted, the flame, for reasons already assigned, 
returns upon the stream of gas, and the combustion, which was 
before imperfect, is then complete. 
How far the fact may be susceptible of a practical applica- 
tion, I am not at present prepared to offer an opinion; but the 
consumption of the gas is, by this mode of burning, very con- 
siderable, and I have not yet been able to determine that there 
is in the combustion of gas under the ordinary pressure, any in- 
crease of illuminating power obtained by inverting the burner. 
—Annals of Philosophy. 
ON THE INVISIBILITY OF CERTAIN COLOURS TO CERTAIN EYES. 
A variety of cases have been recorded, where persons with 
sound eyes, capable of performing all their ordinary functions, 
were incapable of distinguishing certain colours ; and what is 
still more remarkable, this imperfection runs in particular fa- 
Vol. 67. No. 334. Feb. 1826. U milies, 
