154 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



hand, consists principally of bands. In both cases the sim- 

 plest spectra correspond to the least density, and the complex 

 spectra, as well as the continnous spectrnm, correspond to" 

 the condition of greatest density. 



2. The heat necessary in order to act npon a compound 

 body so as to render its spectrum visible, decomposes it by 

 reason of its volatility. The number of true metallic rays 

 that appear augment, therefore, in proportion to the disso- 

 ciation, and, in j^roportion as the metallic rays increase in 

 number, the bands diminish. Applying these considerations 

 to the spectrum of the sun and the stars, Lockyer concludes 

 that the general appearance of the solar spectrum shows that 

 in all probability it is not a compound of the spectra of com- 

 pound bodies. The spectra of the stars, as drawn by Secchi, 

 prove, in Lockyer's opinion, the certainty of the existence of 

 composite vapors in the atmosphere of some of the stars, and 

 one can suppose that the changing appearances of a variable 

 star are due to the state of unstable equilibrium in the tem- 

 perature of this star, which would produce at one time a 

 great absorption of compound molecules or of metalloids, at 

 another time a feeble absorption of elementary molecules. 

 6^,1873,1400. 



DIFFRACTION GKATIXGS. 



Professor C. A. Young, of Dartmouth College, has suggested 

 that the gratings made by ruling fine lines at equal distances 

 on a 'plate of glass may advantageously replace the prisms 

 of the spectroscope designed for the observation of the solar 

 prominences through the Frauenhofer line C. Mr. Ruther- 

 ford has recently furnished Professor Young Avith such a 

 ruled surface of glass, the lines of which are at such an inter- 

 val that six thousand four hundred and eighty of them are 

 contained within the space of one inch. Substituting this 

 for the prism of the common spectroscope. Young obtains a 

 spectrum of the first order, and in wdiich the T> lines are about 

 twice as widely separated as by the original instrument; in 

 the neighborhood of the C line, the dispersion is nearly four 

 times as great. On applying the new instrument to his 

 equatorial telescope, he finds that he can easily see the bright 

 lines of the solar chromosphere; and on opening the slit of the 

 spectroscope, he perceives the outline of the chromosphere. 



