1865.] Draper on American Contributions to Spectrum-Analysis. 395 



remarks witli the expression of an earnest hope that amongst our 

 scientific readers, who must, indeed, be fully alive to the grave nature 

 of the evils to which attention has been directed, many will be found 

 to give the subject their serious consideration, and who will bring 

 energy and experience to bear in the work of their eradication. 



AMEEICAN CONTRIBUTIONS TO SPECTEUM-ANALYSIS. 



By Henry Draper, M.D., 

 Professor of Natural Science in the University of New York. 



Although the fact that a ray of white light consists of several 

 differently coloured rays has been known since the time of Newton, 

 it is only recently that any use has been made of it, in attempting to 

 determine with precision the chemical composition of substances, 

 from the characteristics they impart to flames. A long stage of pre- 

 paration for perfecting such discoveries is necessary, and a multitude 

 of preliminary observations have to be grouped and digested. Even- 

 tually, some striking application of the knowledge thus gained arises, 

 and the subject becomes popular among scientific men, who had failed 

 to see any interest in the previously isolated experiments. It was not, 

 for instance, until Bunsen and Kirckoff ascertained the presence of 

 caesium and rubidium in certain mineral waters, by the aid of the 

 spectroscope, that that instrument attracted the attention it deserved. 

 Even the suggestion that by its aid the physical constitution of the sun 

 and stars might be ascertained, had not sufficed to bring it into notice. 



The application of Spectrum-Analysis to Chemistry turns on the 

 fact, that several, if not all, the elements impress a special change on 

 a flame in which they may be volatilizing. In many cases the change 

 is obvious to the eye, while in others it is necessary to pass the 

 light through a prism, in order to observe with precision what has 

 taken place. We have not, as yet, any knowledge of the reason that 

 some bodies in volatilizing give rise to undulations of a particular 

 length, and others to an entirely different group, we merely know that 

 such an element as sodium, for exanrple, causes vibratory movements, 

 whose length is a definite fraction of an inch, and which pulsate a 

 given number of times in a second, and that no other element can do 

 the same. Whether the hypothesis of Professor Hinrichs of the Iowa 

 University, that the discovery of the laws governing the distribution 

 of the spectral lines will lead to a knowledge of the relative dimen- 

 sions of atoms will turn out to be true or not, remains to be seen. 

 If it be true, Optics would do for the determination of the form and 

 size of atoms, what Chemistry has done for the determination of their 

 relative weights. 



The earliest American experiments in relation to the Constitution 

 of Flames, the Solar Spectrum, &c, were published by Professor 

 John W. Draper, in the ' Philosophical Magazine,' ' Silliman's 

 Journal,' and ' The Journal of the Franklin Institute,' commencing in 



