1874.] Mr. J. N. Lockyer's Spectroscopic Notes. No. III. 375 



2. We start with the following facts : 



I. All elements driven into vapour by the induced current give line- 



spectra. 



II. Most elements driven into vapour by the voltaic arc give us the 



same. 



III. Many metalloids when greatly heated, some at ordinary tem- 

 peratures, give us channelled-space spectra. 



IV. Elements in the solid state give us continuous spectra. 



3. If we grant that the spectra represent to us the vibrations of dif- 

 ferent molecular aggregations (this question is discussed in Note II.), 

 spectroscopic observations should furnish us with facts of some import- 

 ance to the inquiry. 



4. To take the lowest ground. If, in the absence of all knowledge on 

 the subject, it could be shown that all vapours at all stages of temperature 

 had spectra absolutely similar in character, then it would be more likely 

 that all vapours were truly homogeneous and similar among themselves, 

 as regards molecular condition, than if the spectra varied in character, not 

 only from element to element, but from one temperature to another in 

 the vapour of the same element. 



5. At the temperature of the sun's reversing layer, the spectra of all 

 the elements known to exist in that layer are apparently similar in cha- 

 racter that is, they are all line-spectra ; hence it is more probable that 

 the vapours there are truly homogeneous, and that they all exist in the 

 same molecular condition, than if the spectrum were a mixed one. 



6. The fact that the order of vapour-densities in the sun's atmosphere, 

 which we can in a measure determine by spectroscopic observations, does 

 not agree with the order of the modern atomic weights of the elements, 

 but more closely agrees with the older atomic weights, led me to take up 

 the present research. Thus I may mention that my early observations of 

 the welling-up of Mg vapour all round the sun above the Na vapour have 

 lately been frequently substantiated by the Italian observers ; so that it 

 is beyond all question, I think, that, at the sun, the vapour-density of Mg 

 is less than that of Na. 



7. The vapour-densities of the following elements have been experi- 

 mentally determined : 



H 1 S 32 (at 1000) 



K .... 39 I 127 



As .... 150 Hg 100 



Br . . . . 80 N 14 



Cd . . . . 56 O 16 



Cl .... 35-5 P 62 



8. To pursue this inquiry the following arrangements have been 

 adopted : 



The first experiments were made last December upon Zn in a glass 



VOL. XXII. 2 G 



