Analysis by Spectrum-observations. 109 



The dark line D can be produced in the spectrum of a platinum 

 wire heated in a flame, by holding between flame and spectrum 

 a test-tube containing some sodium amalgam which is heated to 

 boiling. This experiment is important, because it shows that 

 sodium vapour at a temperature much below that at which it 

 becomes luminous, exerts its absorptive power at exactly the same 

 point of the spectrum as it does art the highest temperatures 

 which we can produce, or at the temperatures existing in the 

 solar atmosphere. 



We have succeeded in reversing the bright lines in the spectra 

 of Ka, Sr, Ca, Ba, by employing sunlight and mixtures of the 

 chlorates of these metals with milk-sugar. A small iron trough 

 was fixed in front of the slit of our apparatus, in which the mix- 

 ture was placed ; the direct sunlight was then allowed to fall 

 along the whole length of the trough, and the mixture ignited 

 with a heated wire. The telescope C, with the wires cutting 

 each other at an acute angle, was placed so that the point of in- 

 tersection of the wires coincided with the bright line of the 

 flame-spectrum which was to be examined. The observer con- 

 centrated his attention upon this point, to judge whether, at the 

 moment of burning the mixture, a dark line showed itself pass- 

 ing through the point of intersection of the cross wires. In this 

 way it was easy, when the right proportions for the mixtures 

 were found, to show that the lines Ba «, Ba /3, as well as the 

 line Ka /3, were reversed. The last of these lines coincides with 

 one of the most distinct dark lines in the solar spectrum, though 

 not marked by Fraunhofer, which, however, appears much more 

 plainly than it is generally seen at the moment the potash salt 

 burns. In order to prove that the strontium lines can be re- 

 versed, the chlorate of strontium must be most carefully dried, 

 as the slightest trace of moisture produces a positive strontium 

 spectrum, owing to the small particles of salt being thrown 

 about in the flame, and thus diminishing the power of the solar 

 rays. 



We have, in the present memoir, contented ourselves with 

 such an examination of the spectra of the metals of the alkalies 

 and alkaline earths as was necessary for the analysis of terrestrial 

 matter. We reserve for a future communication the further 

 applications of the spectrum-analytical method to terrestrial 

 matter, and to the analysis of the atmospheres of the stars. 



