TOTAL ECLIPSE OF THE SUN, APRIL 16, 1893, 
603 
The “ Reversing Layer” 
As a result of solar spectroscopic observations, combined with laboratory work, 
Dr. Feankland and myself came to the conclusion, in 1869, that at least in one 
particular Kirchhoff’s theory of the solar constitution required modification. In 
that year we v 7 rote as follows'" :—“ May not these facts indicate that the absorption 
to which the reversal of the spectrum and the Fraunhofer lines are due takes place 
in the photosphere itself, or extremely near to it, instead of in an extensive outer 
absorbing atmosphere ?” 
In an early observation of a prominence on April 17, 1870, I found hundreds of 
the Fraunhofer lines bright at the base, and remarked that “ a more convincing 
proof of the theory of the solar constitution put forward by Dr. Frankland and 
myself could scarcely have been furnished.”! 
During the eclipse of 1870, at the moment of disappearance of the sun, a similar 
reversal of lines was noticed ; we had, to quote Professor Young, “ a sudden reversal 
into brightness and colour of the countless dark lines of the spectrum at the com¬ 
mencement of totality.” On these observations was based the view that there was a 
region some 2" high above the photosphere, which reversed for us all the lines 
visible in the solar spectrum; and on this ground the name “reversing layer” was 
given to it. 
Continued observations, however, led me, in 1873, to abandon the view that the 
absorption phenomena of the solar spectrum are produced by any such thin stratum, 
and convinced me that the absorption took place at various levels above the photo¬ 
sphere. I need not give the evidence here; it is set forth in my ‘ Chemistry of the 
Sun.On the latter hypothesis, the different vapours exist normally at different 
distances above the photosphere according to their powers of resisting the dissoci¬ 
ating effects of heat.§ 
My observations during the eclipse of 1882. in the seven minutes preceding totality, 
to my mind set the matter at rest. “We begin with one short and brilliant line 
constantly seen in prominences, never seen in spots. Next, another line appears, also 
short and brilliant, constantly seen in prominences; and now, for the first time, 
a longer and thinner line appears, occasionally noted as widened in spots; while, 
last of all, we get very long, very delicate relatively, two lines constantly seen 
widened in spots, and another line not seen in the spark and never yet recorded as 
widened in spots.” || 
Similar observations in the same part of the spectrum were made by Professor 
* ‘ Roy. Soc. Proc.,’ vol. 17, p. 88. 
t ‘ Roy. Soc. Proc,,’ vol. 18, p. 358. 
J Chapter xxii., pp. 303-309. 
§ ‘ Roy. Soc. Proc.,’ vol. 34, p. 292. 
|| ‘ Roy. Soc. Proc.,’ vol. 34, p. 297. 
4 H 2 
