1869.] Messrs. Frankland and Lockyer on Gaseous Spectra. 79 



which ascribes the appearances to anything but selective plus general ab- 

 sorption, is erroneous. But as I was not aware that it had ever been pro- 

 pounded, I can only refer to my own prior papers in support of my asser- 

 tion, and to Mr. Huggins's indorsement of my observations, which were 

 communicated to the Royal Society some three years ago. 



II. " Researches on Gaseous Spectra in relation to the Physical Con- 

 stitution of the Sun, Stars, and Nebulse." — Third Note. By E. 

 Frankland, F.R.S., and J. Norman Lockyer, F.R.S. Re- 

 ceived July 14, 1869. 



1 . It has been pointed out by one of us that the vapours of magnesium, 

 iron, &c. are sometimes injected into the sun's chromosphere and are then 

 rendered sensible by their bright spectral lines *. 



2. It has also been shown (1) that these vapours, for the most part, 

 attain only a very low elevation in the chromosphere, and (2) that on rare 

 occasions the magnesium vapour is observed like a cloud separated from the 

 photosphere. 



3. It was further established on the 14th of March, 1869, and a draw- 

 ing was sent to the Royal Society indicating, that when the magnesium 

 vapour is thus injected the spectral lines do not all attain the same height. 



Thus of the b lines, b l and b 2 are of nearly equal height, but 6 4 is much 

 shorter. 



o 4. It has since been discovered that of the 450 iron lines observed by 

 Angstrom, only a very few. are indicated in the spectrum of the chromo- 

 sphere when iron vapour is injected into it. 



5. Our experiments on hydrogen and nitrogen enabled us at once to 

 connect these phenomena, always assuming, as required by our hypothesis*)", 

 that the great bulk of the absorption to which the Fraunhofer lines are due 

 takes place in the photosphere itself. 



It was only necessary, in fact, to assume that, as in the case of hydrogen 

 and nitrogen, the spectrum became simpler where the density and tempe- 

 rature were less, to account at once for the reduction in the number of 

 lines visible in those regions where, on our theory, the pressure and tem- 

 perature of the absorbing vapours of the sun are at their minimum. 



6. It became important, therefore, to test the truth of this assump- 

 tion by some laboratory experiments, the preliminary results of which we 

 beg to communicate in this Note, reserving details, and an account of the 

 further experiments we have already commenced, for another paper under 

 the above title. 



We took the spark in air between two magnesium poles, so separated 

 that the magnesium spectrum did not extend from pole to pole, but was 

 visible only for a little distance, indicated by the atmosphere of magnesium 

 vapour, round each pole. 



* Proc. Koy. Soc. vol. xvii. p. 351. 



f Ibid. p. 290. 



