38G 
MR. J. EYERSHED OX ’\YAYE-LENGTIi DETERMIXATIOXS, ETC., 
I was obsei’ving with a slitless spectiosco 2 )e attached to a 3-iiich equatorial, and 
made the exposure as nearly as I could judge 2 seconds before the last trace of 
continuous spectrum vanished. The jilate was given an exposure of at least 4 seconds 
in order to impress the fainter details. 
In the photograph the strip of continuous spectrum is divided into four parts by 
longitudinal dark bands due to irregularities in the moon’s limb. Most of the bright 
lines of the chromosphere and flash spectra are visible as bright lines upon the 
continuous spectrum, but tlie helium lines at X 4026'5 and X 4713‘2 are an exception, 
and they cannot be traced even in the dark sj^aces between the strips of continuous 
spectrum, although strongly impressed on either side. The helium line at X 4472 is 
visible, but weaker in the inteiinediate dark spaces. No trace of any absorption lines 
can be detected in any part of the continuous spectrum. 
The total depth of the chromos})here as indicated by the calcium lines H and K is 
lR’‘G, these lines extending over an arc of 124 degrees. The hydrogen lines y, S, ?, 
and the titanium lines at X 3761'5, X 3759'3, and X 3685'3, as well as the helium 
line D"', extend over an arc of about 102 degrees, inq^lying a depth of 8"'2. 
The bright arcs of the flash spectrum proper are approximately of the same length. 
On the north side of the continuous spectrum they are cut off abruptly by a dark 
band, due to a projecting lunar mountain, and two similar bands interrupt the lines on 
the south side. 
Most of tlie fainter flash lines can Ije traced over an arc of 40 degrees of the sun’s 
limb, indicating a depth of 1"‘3, or nearly 600 miles. 
A great many of the stronger lines, however (chiefly titanium, iron, and magnesium 
lines), extend faintly far beyond this limit, and can be traced over an arc of nearly 
70 degrees, the depth implied in this case exceeding 4", or 1800 miles.^ 
A few very faint lines due to the very lowest layers of the chromosphere are also 
indicated in the best defined portion of the negative. These are visible only upon the 
strips of continuous sjiectrum, and do not extend beyond. 
Probably oul}^ a small j)roportion of the finer lines which were actually present at 
second contact are shown in this })hotograph. In the green region near h this is 
certainly the case. The most striking feature seen when observing the spectrum 
under high dis})ersion and without any slit was the immense number of excessively 
fine bright arcs which appeared in a short section of the spectrum (including the 
b lines) at'the moment 'when the exposure was made. Yet very few of these lines 
appear on the photograph, partly })erhaps on account of the poor focus in this region. 
* [111 estimating depths from the lengths of the arcs the moon’s apparent semi-diameter is taken at 
997"'0 and that of the sun 974"'9. A uniform distribution of the gases round the limb is of course 
assumed, and the results from Xo. 3 spectrum indicate the dejith measured from the photosphere to the 
upper limit to which each particular radiation can be traced. The depth of photosphere left uncovered 
by the moon in this photograph being quite inappreciable, the limit of the moon may be considered as 
being coincident rvith that of the sun at the point of second contact .—March 9, 190L] 
