seen at a glance. The matching and identification are even more complete than they were in the original experiments of Kirchhoff with the metals, for here it is not necessary to invoke a theory for the unification of bright and dark lines; the bright lines of the spectrum of oxygen being continuous with the bright lines of the solar spectrum. It is, indeed, because the solar oxygen reveals itself by bright lines that these have not been earlier detected, as they have been masked and concealed among the unoccupied luminous spaces, between the dark lines that have hitherto been the main objects of attention.
Dr. Draper has been occupied for several years with this investigation—in fact, he has grown into it. Besides Lis inherited attitude, and life-long training in this delicate line of manipulation, and his thorough familiarity with the peculiar difficulties of these investigations, his work could only have become successful by means of a combination of appliances, some of which are only lately available. His task was to produce a gas spectrum, and maintain it at a brilliancy which would admit of its being photographed alongside of that of the sun itself. Oxygen is made incandescent by electricity. The most ample, steady, and sustained command of this agent was therefore indispensable. This was secured by the Gramme machine, a dynamo-electric engine connected with a large induction-coil and a battery of Leyden-jars. The impulse was furnished by a Brayton's petroleum-motor, which "can be started with a match, comes to its regular speed in less than a minute, and preserves its rate entirely unchanged for hours together." This was belted to the Gramme machine, which, at its usual rate of running, gave 1,000 ten inch sparks per minute. This "torrent of intense electric fire," consisting of twenty ten-inch sparks per second, was passed through Plücker's tubes, containing oxygen, the spectrum of which is thrown upon a sensitive photographic surface, while the solar spectrum is formed beside it, and both are fixed together upon the tablet. The embarrassments of the investigation are thus referred to in Dr. Draper's paper:
In regard to the significance of the inquiry in relation to spectroscopic study, Dr. Draper remarks: