256 = od. C. Draper—Dark Lines in the Solar Spectrum. 
made of an inverted glass shade filled with water. This form of 
condenser was first use r. R. M. Ferguson, of Edinburgh. 
Fig. 1 shows the arrangement of the experiment. The rays 
of light, R, from a heliostat, or from an oxyhydrogen light, fal 
on an inclined mirror, A, placed under the water condenser C. 
The needles float on the surface of the water in this condenser. 
The rays which have passed through the lens, L, are reflected 
by the swinging mirror, B, to the distant screen, where they 
form the images of the floating magnets. The magnet is held 
over the needles at M, by means of a wire which is wrapped 
round the magnet to serve asa handle. Ifa long magnet be 
used it will work well if its pole is brought over the needles* 
by inclining it. 
hese experiments with floating magnets give forcible pre- 
sentations of the reign of law. It is indeed quite impressive 
to see order being evolved out of chaos as we hold a magnet 
over a number of needles, carelessly thrown on water, and wit- 
ness them approaching and, one after the other, entering into 
the structure of that geometric figure which conforms to the 
number of magnets composing it. 
Art. XXVIIL— On the presence of Dark Lines in the Solar 
Spectrum, which correspond closely to the lines of the Spectrum 
of Oxygen; by JoHN CHRISTOPHER Draper, M.D., LL.D., 
Professor of Natural History in the College of the City of 
New York. 
THE measurement of the wave lengths of the dark lines of 
the solar spectrum obtained by photographs, and the construc- 
tion of a chart of the same, has for many years occupied m 
leisure time. As a result of the investigations connected wit 
this work, I have arrived at the belief that oxygen as well as 
other non-metallic gaseous elements are represented in the 
solar spectrum by dark lines, in the same manner as metallic 
substances. The lines in the case of oxygen are however very 
faint, when compared with those produced by metals in the 
vaporous state. 
The apparatus employed in these investigations may be 
briefly described as detliowee: 1st, a spectroscope for photo- 
graphing the normal solar spectrum. As my purpose was to 
obtain photographs in which the positions of the lines should 
be as true as possible, I resorted entirely to the process 
reflection, and at no time did the solar rays pass through glass ; 
* The magnetic needles in the experiments miay be replaced s of soft 
iron wire Which will be maguaaided be Ghartasceion a6 the Sipura wagem 
& 
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