368 Dr. J. A. Fleming on the Characteristic Curves 
across the spectrum, and with a small flame a marked thicken- 
ing of the dark line is seen just above the spoon. ‘The sodium 
may be burnt in a Bunsen burner or in the flame of a spirit- 
lamp. 
If the sodium-flame is placed between the slit and the lime- 
light, I have obtained a good result by using a Bunsen burner, 
the flame of which is cooled down to a proper temperature by 
a mixture of airand carbon dioxide. Care must be taken not 
to pass carbon dioxide into the flame to excess, otherwise too 
great a lowering of its temperature takes place. I have, for 
instance, obtained in this manner a bluish flame which did 
not show the slightest trace of sodium in a room where suf- 
ficient sodium had been burnt to make every gas-flame give 
a strong sodium reaction. 
The supply of carbon dioxide to the Bunsen burner may be 
adjusted in the following manner :—A cork is attached to the 
movable cover which closes the two holes for admitting air, 
and two holes made in it opposite the air-holes; to one a 
glass tube is attached which is connected with a bottle, into 
which carbon dioxide is passed, fitted with three openings. 
By opening clamps the carbon dioxide may be all passed into 
the Bunsen burner, or passed directly out from the bottle. 
The sodium is first brought into vivid combustion, and then 
the flame cooled down by admission of the proper supply of 
carbon dioxide. 
The reversed line may also be shown by burning sodium in 
a spirit-lamp with four wicks, in the centre of which is a jet 
for the admission of oxygen. This is placed between the 
slit and the limelight. On passing oxygen into the flame, 
the heat may be raised sufficiently high to produce a bright 
Na band upon the screen, especially if the light from the 
incandescent lime is somewhat moderated, and turned into a 
dark band when the oxygen is shut off, proving that the 
production of a dark or bright sodium-band depends upon 
the temperature of the absorbent vapour. 
XL. On the Characteristic Curves and Surfaces of Incan- 
descence Lamps. By J. A. Fuemine, M.A., D.Sc. (Lond.), 
Fellow of St. John’s College, Cambridge*. 
eee issues of a scientific journal? have contained 
some interesting letters and notes on the life of incan- 
descence lamps, and on resulting deductions to be made 
* Communicated by the Physical Society: read March 14, 1885. 
+ ‘The Electrician, vol. xiv. (1885), pp. 246, 294, 311, 347. 
