NATIONAL ACADEMY OF SCIENCES. 



A strip of that metal one inch long and one-twentieth of an inch 

 wide, connected with a lever by which its expansion might be meas- 

 ured, would yield at 2,000 a light suitable for most purposes. More- 

 over, it would be very^easy to form from it a photometer by screen- 

 ing portions of the shining surface. An ingenious artist would have 

 very little difficulty, by taking advantage of the movements of the 

 lever, in making a self-acting apparatus, in which the platinum 

 should be maintained at a uniform temperature, notwithstanding any 

 change taking place in the voltaic current." 



In the following year Dr. Draper published a noteworthy memoir 

 on the production of light by chemical action. In this memoir he 

 investigates by means of the prism the character of the light which 

 is produced by combustion, answering thus his own query, " Can 

 any connection be traced between the chemical nature of a substance 

 or the conditions under which it burns and the nature of the light 

 which it emits ?" With a slit, a prism, and an observing telescope 

 he examined the flames of oil, of alcohol, of alcoholic solutions 

 of boric acid and strontium nitrate, of phosphorus, of sulphur, of 

 carbonic oxide, of hydrogen, of cyanogen, and of arsenetted hydro- 

 gen. The flame of the oil was yellow ; of the alcohol, pale blue ; of 

 the boric acid, green; of the strontium, red; of the phosphorus, 

 yellowish white; of the sulphur and carbonic oxide, blue; of the 

 hydrogen, pale yellow ; of the cyanogen, lilac, and of the arsenetted 

 hydrogen, white. "Notwithstanding this diversity of color," he 

 says, "all these flames, as w T ell as many others that I have tried, 

 yield the same result; every prismatic color is found in them. Even 

 in those cases where the flame is very faint, as in alcohol and in hy- 

 drogen gas, not only may red, yellow, green, blue, and violet light 

 be traced, but even bright Fraunhoferian lines of different colors." 

 The spectra given by these variously-colored flames were carefully 

 drawn and their peculiarities were pointed out. When, he thus 

 examined the flame of cyanogen he beheld, as he says, " a spectrum 

 so beautiful that it is impossible to describe it by words or depict it 

 in colors. It was crossed throughout its extent by black lines sep- 

 arating it into well-marked divisions. I could plainly count four 

 red rays of definite refrangibility, followed by one orange, one yel- 

 low, and seven green rays, while in the more refrangible spaces were 

 two extensive groups of black lines, recalling somewhat from their 

 position, but greatly exceeding in extent, Fraunhofer's lines G and 

 H in the sun's rays." He considered the interior lilac cone to be 



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