You smile, and possibly think that Homer's Iliad is
good as a means of culture. There's the rub. The people who demand
of science practical uses, forget, or do not know, that it also is
great as a means of culture--that the knowledge of this wonderful
universe is a thing profitable in itself, and requiring no practical
application to justify its pursuit.

But while the student of Nature distinctly refuses to have his labours
judged by their practical issues, unless the term practical be made to
include mental as well as material good, he knows full well that the
greatest practical triumphs have been episodes in the search after
pure natural truth. The electric telegraph is the standing wonder of
this age, and the men whose scientific knowledge, and mechanical
skill, have made the telegraph what it is, are deserving of all
honour. In fact, they have had their reward, both in reputation and
in those more substantial benefits which the direct service of the
public always carries in its train. But who, I would ask, put the
soul into this telegraphic body? Who snatched from heaven the fire
that flashes along the line? This, I am bound to say, was done by two
men, the one a dweller in Italy, [Footnote: Volta] the other a
dweller in England, [Footnote: Faraday] who never in their enquiries
consciously set a practical object before them--whose only stimulus
was the fascination which draws the climber to a never-trodden peak,
and would have made Caesar quit his victories for the sources of the
Nile. That the knowledge brought to us by those prophets, priests,
and kings of science is what the world calls 'useful knowledge,' the
triumphant application of their discoveries proves. But science has
another function to fulfil, in the storing and the training of the
human mind; and I would base my appeal to you on the specimen which
has this evening been brought before you, whether any system of
education at the present day can be deemed even approximately
complete, in which the knowledge of Nature is neglected or ignored.

********************

IV. NEW CHEMICAL REACTIONS PRODUCED BY LIGHT.

1868-69.

1 DECOMPOSITION BY LIGHT.

MEASURED by their power, not to excite vision, but to produce heat--in
other words, measured by their absolute energy--the ultra-red waves of
the sun and of the electric light, as shown in the preceding articles,
far transcend the visible. In the domain of chemistry, however, there
are numerou