FLxiME SPECTRA AT HIGH TEMPERATURES. 
1047 
spiegel-eisen. This examination convinced me that the banded spectrum of carbon 
is never visible, and that the l^ands which are seen in the spiegel spectrum possess a 
feature which distinguishes them in a striking manner from the bands of carbon, 
namely, they are degraded towards the red, the carbon bands being degraded towards 
the blue. This had already been noticed by Watts. 
Dcsc7'i2')tion of the Instrument used and the method, of observing and photographing 
Spectra of the Bessemer Flame. 
In 1882 I devised an instrument for meeting the requirements of a series of 
observations to be made at steel works, particularly for studying the spectra of 
flames, and the heated gases of open-heartli furnaces. It was desirable that it should 
give a fair amount of dispersion at the less refrangible end of the spectrum, be rigid 
and portable. A train of four quartz prisms was at first arranged on a table and 
stand made entirely of wood, to which a camera was fitted, with a rack and pinion 
movement to the frame holding the dark slide, so that several spectra could be 
photographed on one plate. Various trials with this mounting showed that owing to 
the stand being too light, the instrument was unsteady. In 1887 the quartz train 
was mounted on a heavy tripod stand. The prism table was fixed to the pillar of the 
stand by a winged screw joint and counterpoised, so that it could be placed in almost 
any required position. The camera was of metal, with an eye-piece behind the frame 
for the dark slide, so as to make it available for observations with the eye, for which 
it is peculiarly well adapted, owing to the observer having the flame behind him, and 
therefore he is not embarrassed by the glare. In the circular box at tlie end of the 
camera the dark slide can be fixed at any angle, as it is rotated by means of 
a toothed wheel. The collimator and telescope or camera are fitted with a scale 
of millims. on the draw-tubes, so that botli the slide and photographic plate may be 
drawn out so as to be equi-distant from the lenses for the purpose of focussing 
correctly. The camera can be clamped, and its exact position determined by means 
of a divided arc on the prism table. A telescope with a photographic scale, which is 
reflected from the face of that prism which is nearest to the lens in the camera, has 
been found useful. The prisms move automatically with the camera, in order to 
secure the minimum angle of deviation for the mean rays photographed. A frame¬ 
work in front of the slit, and fixed to the prism table, carries a condensing lens of 
three inches focus. Latterly, a condenser with two cylindrical lenses crossed at right 
angles has been in use, a device which was described in a letter to the author by 
Herr Victor Scijumann. If has the advantage of giving a very sharp image of the 
lines, but it was not employed at Crewe, or at Dowlais, owing to the fitting bemg a 
delicate one, the adjustment requiring care, and the necessity which occasionally 
arises for cleansing the condensing lenses from time to time from dusty fume, or 
moisture, even during the progress of the “ blow.” With the usual form of condenser. 
