ON STELLAR SPECTROMETRY. 165 
not sufficient to support the conclusion that no part of the light of the umbra 
is from such a source. The luminous gas would emit light of the same re- 
frangibility as some of the dark lines of the solar spectrum. If these existed 
above the same substance in a cooler state, the light might be absorbed, and 
the feebler emanations of the still luminous but cooler vapours might not 
do more than render less intense the dark gaps produced by the vapours on 
the stronger light of all refrangibilities which is also present. What may 
be the source of this light we do not know. It is not impossible that the 
dense and intensely heated gases which probably form the inner substance of 
the sun may in some cases emit lines so greatly expanded as to form, when 
humerous spectra are superposed, a sensibly continuous spectrum, Gases, 
when dense, appear to give a continuous spectrum, in addition to that con- 
sisting of bright lines. 
§ V. OBsERVATIONS OF THE PLANETS. 
Mars.—In a paper presented to the Royal Astronomical Society in March 
1867*, I gave the results of a further examination of the spectrum of Mars. 
In that paper I describe more fully than in my former papers the lines in 
the spectrum of this planet, which show the existence of an atmosphere 
similar to that of the earth, though probably not identical with it. 
I give reasons which appear to show that the distinctive ruddy colour of 
the planet is not to be attributed to the absorptive properties of its atmo- 
sphere, but to some peculiarity which attaches to certain parts of its surface. 
Neptune.—I have several times observed the spectrum of Neptune, but 
failed to detect any very marked lines of absorption which might account 
for the blue colour of the planet. The faintness of its spectrum does not 
permit any great value to be attached to this negative result. 
On Stellar Spectrometry. By Padre Snccurt. 
Fravnnorer was the first to analyze with the prism the light of some of the 
stars. He discovered in them lines analogous to those which he had dis- 
covered in the solar spectrum. Donati, an Italian astronomer now at 
Florence, resumed these researches and extended their field. Several astrono- 
mers followed, and amongst them the distinguished Mr. Huggins, to whom we 
owe a description of the spectra of a great number of stars and the ap- 
plication of the principle of determining the substances contained in a star 
from the black lines of absorption which we see in its spectrum, as was 
proposed by Kirchhoff. Mr. Huggins also made the wonderful discovery of 
the gaseous state of the nebulz. 
The field opened by these discoveries was immense, and even before the 
date of Mr. Huggins’s publications I tried to glean some ears init. In the 
first stage of these studies the principal stars only were examined, the im- 
perfection of my instruments not allowing the examination of all the hea- 
yeuly bodies. 
An optical combination which I had the good fortune to discover, enabled 
me to extend the researches to the whole of the visible stars, and even to 
several telescopic ones, which present perhaps the greatest mysteries of this 
kind. 
* Monthly Notices of the Royal Astronomical Society, vol. xxvii. p- 178. 
t A communication ordered to be printed in extenso. 
