436 ME. J. N. LOCKYEE ON SPEOTEOSCOPIC OBSEEYATIONS OF THE SUN. 
years ago by so excellent an observer as Mr. De La Rue should be found to bear 
independent testimony to the accuracy of the conclusion which I have arrived at, by an 
entirely different line of research. 
Beceived April 9, 1869. 
Historical Notice of the growth of our knowledge of the Chromosphere. 
When I was first enabled, by means of the spectroscope, to determine that the promi- 
nences are merely heapings up of an envelope which gave everywhere the spectrum of 
hydrogen (at pressures which Dr. Frankland and myself have since approximately deter- 
mined) and is continuous round the sun, or at all events continuous in the same sense 
that the photosphere is continuous, I was not aware that I had been anticipated in any 
part of the discovery. 
I have since found, however, that the continuity of the envelope, apart from its nature 
and place in the solar economy, has been suspected for many years, although it had never 
been demonstrated, as it easily might have been, by eclipse observations at properly 
chosen stations, and although it has been very variously interpreted. 
I think it desirable, now that the spectroscope has determined the existence and nature 
of such an envelope, that, injustice to myself and to those who have gone over the same 
ground before me, a brief historical notice of the progress of our knowledge on this 
point should be given. 
It is easy now to divide the phenomena observed in the many eclipses between 1706 
and 1842 into two classes : 
I. Observations of the prominences properly so called ; 
II. Observations of the chromosphere ; 
and all the observations of both these classes, accumulated during the eclipses which 
happened up to and including the year 1842, have been discussed by two eminent astro- 
nomical authorities, — I refer to Arago and Professor Grant, to both of whom, long even 
before the eclipse of 1851, it was perfectly obvious that the prominences were solar and 
not lunar phenomena. 
Arago * considered the prominences to be merely clouds floating in the sun’s atmo- 
sphere — an atmosphere rendered evident to us by the Corona, and to these clouds he 
ascribed the spots without a nucleus ; to the Corona also he attributed the darkening of 
the limb. He says : — 
“ II faut admettre une enveloppe exterieure qui diminue (eteint) moins la lumiere qui 
vient du centre que les rayons qui viennent sur le long trajet du bord a l’ceil. Cette 
enveloppe exterieure forme la couronne blanchatre dans les eclipses totales du soleil.” 
It is not easy to reconcile all Arago’s statements as to the nature of this atmosphere 
or envelope ; but I shall return shortly to a later enunciation of them by himself, merely 
* Annuaire du Bureau des Longitudes, 1846. MSS. quoted by Humboldt, Cosmos, Sabine’s Translation, 
vol. iv. Notes, p. cii. 
