1*23 
for Microscbftcal and other 'purposes. 
As the yellow rays seemed to be the product of an imperfect 
combustion, I conceived that alcohol diluted with water would 
produce them in greater abundance than when it was in a state 
of purity, and upon making the experiment, I found it to suc- 
ceed beyond my most sanguine expectations. The whole of the 
flame, with the exception of a small portion of blue light, was a 
fine homogeneous yellow^ which, when analysed by the prism, 
exhibited faint traces of green and blue, but not a single ray of 
red or orange light. The green and blue rays which accom- 
panied the yellow flame, had comparatively so little intensity,, 
that they disappeared in the processes of illuminating and mag- 
nifying the object under examination ; and, even if they had 
existed in greater abundance, it v/as quite easy to .absorb them 
at once by the intervention of a plate of the palest yellow glass, 
and thus render the lamp perfectly monochromatic. 
From many experiments on the combustion of diluted alco- 
hol, I found that the discharge of yellow light depended greatly 
on the nature of the wick, and on the rapidity with which the 
fluid was converted into vapour. A piece of sponge, with a 
number of projecting points, answered the purpose of a wick 
better than any other substance, and the extrication of the yel- 
low light became more copious, by placing a common spirit-lamp 
below the burner of the other. In order to obtain a very strong 
light for occasional purposes, I connected with the top of the 
burner a frame of wire-gauze, which, by moving vertically round 
a hinge, or by a motion to one side, could be placed in a hori- 
zontal position about half an inch above the wick. As soon -as 
it had become red-hot, it was made to descend into contact with 
the sponge, when it converted the alcohol rapidly into vapour, 
and produced an abundant discharge of yellow light. See Plate 
II. Fig. 5. 
If a permanently strong light is required, I find it preferable 
to dispense entirely with the use of the wick, and to allow the 
diluted alcohol to descend slowly from the rim into the bottom 
of a concave dish of platinum, kept very hot by a spirit-lamp 
placed beneath it. The bottom of the dish is made with a num- 
ber of projecting eminences, in order that the film of fluid which 
rests upon it may be exposed at many points to the action of the 
heated surface. See Fig. 6. After the lamp has burned for 
