SPUCTR OSCOPl C DIS CO VER F. 431 



If the non-metallic elements, it was said, which form the principal part of 

 terrestrial objects, do not exist in the sun, the derivation of that body and of 

 its encircling planets from the same primeval source is impossible. Dr. 

 DrajDer has now proved that oxygen in large proportions exists in the sun 

 (and probably nitrogen also) ; and his discovery can therefore only be 

 regarded as lending further and more powerful confirmation to the nebular 

 hypothesis. 



Dr. Draper's paper, in the American Journal of Science and Arts, is accom- 

 panied by an illustrative diagram, which brings the demonstration before 

 the eye of every reader. It exhibits the spectrum of the sun, and that which 

 is produced from air, so juxtaposed that the fact and the extent of the iden- 

 tity of the lines in the two representations are 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 in- 

 voke 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 his inherited aptitude, 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 elec- 

 tricity. The most ample, steady, and sustained command of this agent was 

 therefore indispensable. This was secured by the Gramme machine, a 

 dynamo-electric engine connectedwith a large induction-coil and a battery 

 of Leyden-jars. The impulse was furnished by a Brayton 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 

 Vv^as 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 Pliick- 

 er'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 : 



"This research has proved to be more tedious and difiicult than would 

 be supposed, because so many conditions must conspire to produce a good 

 photograph. There must be a uniform, prime-moving engine of tvvo-horse 

 power, a dynamo-electric machine thoroughly adjusted, a large EuhmkoftV 



