430 ME. J. N. LOCKYER ON SPECTROSCOPIC OBSERVATIONS OF THE SUN. 
On the 5th of November I obtained the outline of two brilliant prominences, one 
near the southern, the other near the northern limb of the sun. The extreme (measured) 
apparent height of one was 35,000 miles, of the other somewhat less ; the former I 
estimated to extend along the sun for about 200,000 miles, The shape of the southern 
prominence had changed considerably by the next day, the bright peak being quite gone ; 
at the same time the length of the main portion had extended as if the peak had been 
absorbed into it (Plate XXXVII. figs. 8 & 9). 
The prominences therefore change from day to day ; at present I have not measured 
any more rapid change, but these observations are of so delicate a nature that it is easy 
to imagine rapid changes to be going on in any prominence of decided outline ; for an error 
in the adjustment of the instrument with regard to the meridian or latitude, the least 
variation in the rate of the driving-clock, or any oscillation of the telescope-tube or 
the spectroscope, brings the slit on another part of the outline of the prominence, and 
under these circumstances the length of the line is perpetually varying. 
It must be borne in mind that the dimensions of the prominences cannot be deter- 
mined absolutely, as we do not know whether they are actually on the sun’s limb at the 
time of measurement. Measurement can only fix a minimum. 
On the Continuous Solar Envelopes. 
The continuity of this envelope, which I propose to name the Chromosphere, a name 
suggested by Dr. Sharpey, was spectroscopically established on the 5th of November, 
and an account of the observations was transmitted to the Royal Society on the same day. 
By careful estimations made on the 6th of November (which are estimations only, 
for I had not yet mounted a wire-micrometer on the spectroscope-telescope), its general 
thickness w 7 as determined to be about 5000 miles ; the level of its upper surface was not 
absolutely uniform in all latitudes, but it was very nearly so. I could detect no dif- 
ference in the general level as between the equatorial and solar regions of the sun. 
It would appear that the light by which its existence is revealed proceeds from the 
same substance or substances of which the prominences are composed ; and I hold the 
prominences to be merely the heaping together of the new envelope in some localities. 
Under proper instrumental conditions the spectrum of this envelope can always 
be seen whenever the sun is shining. The spectrum consists of a line coincident with 
Fraunhofer’s C, another more refrangible than D, and another coincident in the main 
with F. I say coincident in the main, because when the spectrum of the envelope is 
viewed so that it appears to rest on the solar spectrum, the line at F takes the form 
of an arrow-head (Plate XXXVII. fig. 3), the shaft of the arrow being represented by 
the black line F in the solar spectrum itself. This results from a thickening out of the 
line as it approaches the sun. At the outer surface of the envelope the refrangibility 
of the light is the same as that of the line F ; but, as the sun’s surface is approached, 
the line widens gradually into a band overlapping F by more than its own thickness on 
either side, and more on the more refrangible side than on the other. The black line F 
