4 
will include stars ofthe fourteenth magnitude. Many years must of 
course elapse before the completion of the chart. When photography 
was as yet in its infancy, a brilliant future, in connection with 
astronomy, was prophesied for it by Arago, who wrote with 
enthusiasm of a photographic picture he had seen of the moon. 
Since then, lunar photography has developed to such an extent, 
that, according to an American geographer ‘‘ there are many parts 
of the new world less accurately chartered than the “seas ”’ valleys, 
and mountains of the pale inconstant planet.” Photography has 
played a no less important part in revealing to us the nature of the 
sun himself, the corona and the fiery streamers ; indeed, it is now 
some years since Sir John Herschell wrote that, ‘‘the orb of day 
has been compelled to write its own history.”’ 
An important fact disclosed by the spectroscope is, that 
‘ terrestrial matter is not peculiar to the solar system above, but 
is common to all the stars visible to us.” Take, for instance, the 
star Capella, whose spectrum is almost identical with that of the 
sun, and whose constitution and temperature we have therefore 
every reason to suppose is also the same. Professor Rowland has 
shown that the lines of at least thirty-six terrestrial elements are 
present in the solar spectrum ; as to fifteen other elements, there 
is very little evidence that they are absent from the sun, but ten 
others of which oxygen is one, have not yet been compared with 
the sun’s spectrum. Hence we may conclude that if the earth 
were heated to the temperature of the sun, its spectrum would be 
very similar. Professor Rowland is now endeavouring to discover 
by means of these lines in the solar spectrum, which are as yet 
unaccounted for, new terres trial elements which may possibly lurk 
in rare earths and minerals, his method being to compare their 
spectra with that of the sun. It is a curious fact that our know- 
ledge of the spectrum of hydrogen came to us from the spectra of 
the stars, and, in the same way, chemistry is even now seeking for 
new elements in our earth by means of the solar sp: ctrum. 
I may here mention in passing that, Professor Higgins entirely 
confirms Professor Schuster’s theory of the origin of the sun’s 
corona; namely, that it consists of matter, flowing from the sun 
under the influence of some force, probably electricity. Some 
particles of the corona may possibly return to the sun, but the 
greater portion, forming the long “ fiery streamers,” or rays of light 
do not appear to return; they may, not improbably furnish the 
material for the Zodiacal Light, of which no other explanation has 
as yet been offered. 
The spectra of the stars, although greatly diversified, may yet, 
to a certain extent, be classified in groups, the sun’s place being 
apparently in about the middle of the series. Astronomers differ 
