the prominences may be rendered visible in sunshine; and for a
reason easily understood. You have seen in these lectures a single
prism employed to produce a spectrum, and you have seen a pair of
prisms employed. In the latter case, the dispersed white light, being
diffused over about twice the area, had all its colours
proportionately diluted. You have also seen one prism and a pair of
prisms employed to produce the bands of incandescent vapours; but here
the light of each band, being absolutely monochromatic, was incapable
of further dispersion by the second prism, and could not therefore be
weakened by such dispersion.

Apply these considerations to the circumsolar region. The glare of
white light round the sun can be dispersed and weakened to any extent,
by augmenting the number of prisms; while a monochromatic light,
mixed with this glare, and masked by it, would retain its intensity
unenfeebled by dispersion. Upon this consideration has been founded a
method of observation, applied independently by M. Janssen in India
and by Mr. Lockyer in England, by which the monochromatic bands of the
prominences are caused to obtain the mastery, and to appear in broad
daylight. By searching carefully and skilfully round the sun's rim,
Mr. Lockyer has proved these prominences to be mere local juttings
from a fiery envelope which entirely clasps the sun, and which he has
called the _Chromosphere_.

It would lead us far beyond the object of these lectures to dwell upon
the numerous interesting and important results obtained by Secchi,
Respighi, Young, and other distinguished men who have worked at the
chemistry of the sun and its appendages. Nor can I do more at present
than make a passing reference to the excellent labours of Dr. Huggins
in connexion with the fixed stars, nebulae, and comets. They, more
than any others, illustrate the literal truth of the statement, that
the establishment of spectrum analysis, and the explanation of
Fraunhofer's lines, carried with them an immeasurable extension of the
chemist's range. The truly powerful experiments of Professor Dewar are
daily adding to our knowledge, while the refined researches of Capt.
Abney and others are opening new fields of inquiry. But my object here
is to make principles plain, rather than to follow out the details of
their illustration.

SUMMARY AND CONCLUSION.

My desire in these lectures has been to show you, with as little
breach of continuity as possible,