1048 
PROFESSOR W. N. HARTLEY OH 
an image of the flame was projected upon the slit, sometimes the flame was in the 
same vertical line with the slit, and sometimes placed diagonally. This depended 
very much upon the position of the converter and the consequent size of the image. 
I’he slit plate was covered with a thin ])]ate of quartz to exclude dust and dirt. A 
metal j^late with a V-shaped piece cut out of one end slides over this, and serves to 
shorten or lengthen the slit, and secure a greater or smaller number of spectra on one 
photographic plate. In some cases, a photograph was taken eveiy half-minute, from 
the commencement to the termination of the “ blow.” This could be accomplished 
only by the use of such a contrivance, as the plates measured no more than 
3 X 2^ inches. 
To focus the instrument various photographs of sun-spectra were taken and the 
positions of the difterent adjustable parts were recorded. In order to render the 
instrument portable a case was constructed for carrying the prism table, j^risms, 
collimator, and camera, without disarranging the adjustment of the instrument. A 
winged screw when loosened enabled the whole to be detached from the vertical 
pillar of the tripod, the counterpoise, of course, having been detached previously. 
The prism table was then fastened in its case. A second case carried the tripod, 
counterpoise, chemicals, and developing dishes. This case when empty had a square 
frame of wood which fitted into the top when the lid was ojDen. The frame was 
covered with waterproof cloth, lined with yellow calico. In the cloth were arm-holes 
and sleeves fitted with elastic, which came half way up to the elbows. The develoj)ing 
dishes and measured quantities of solution were placed ready in the box and the dark 
slide could be opened, the plate removed and placed in the developer, while during 
development a new })late could be put into the slide. Development was always 
allowed to proceed for a given period which previous experiment had proved to be 
sufficient. During the progress of development the dish was covered with an ebonite 
tray to exclude any possibility of light reaching the photographic plate. By such 
nreans the plates are developed and fixed without the use of a dark room, but it is, of 
course, essential that the hands are not withdrawn from the box before the develop¬ 
ment is concluded. At Crewe my assistant had the use of a laboratory, but at 
Dowlais the operating box was always used. 
Ai-rangements were made for carrying out the first series of observations from a 
point on the floor of the cupola-house at Crewe, situated close to the platform, from 
which the ladles of spiegel-eisen are tipped into the converters. The instrument was 
placed upon a very solid bench, which could, liowever, be moved about as required. 
From preliminary observations with a direct vision instrument it was decided to take 
photographs of the sun-spectrum at the laboratory, to sensitise some plates with 
cyanine, develop the sun-photographs, and, having obtained a good focus, to remove 
the instrument by hand to the cupola-house. It was considered best to photograph, 
first, the spectrum obtained during the whole period of the “ boil,” and, secondly, the 
blaze, after the addition of spiegel-eisen. Unfortunately the sun was not always 
