plication of the photography of the present day, but it is germane
to my purpose to remark that it has furnished a most valuable
accessory to the methods of recording motions and lapse of time
already in existence. In the hands of the astronomer and the
meteorologist, it has yielded means of registering terrestrial, solar,
planetary, and stellar phenomena, independent of the sources of error
attendant on ordinary observation; in the hands of the physicist, not
only does it record spectroscopic phenomena with unsurpassable ease
and precision, but it has revealed the existence of rays having
powerful chemical energy, or beyond the visible limits of either end
of the spectrum; while, to the naturalist, it furnishes the means by
which the forms of many highly complicated objects may be represented,
without that possibility of error which is inherent in the work of the
draughtsman. In fact, in many cases, the stern impartiality of
photography is an objection to its employment: it makes no distinction
between the important and the unimportant; and hence photographs of
dissections, for example, are rarely so useful as the work of a
draughtsman who is at once accurate and intelligent.

[Sidenote: Astronomy,]

The determination of the existence of a new planet, Neptune, far
beyond the previously known bounds of the solar system, by
mathematical deduction from the facts of perturbation; and the
immediate confirmation of that determination, in the year 1846, by
observers who turned their telescopes into the part of the heavens
indicated as its place, constitute a remarkable testimony of nature to
the validity of the principles of the astronomy of our time. In
addition, so many new asteroids have been added to those which were
already known to circulate in the place which theoretically should be
occupied by a planet, between Mars and Jupiter, that their number now
amounts to between two and three hundred. I have already alluded to
the extension of our knowledge of the nature of the heavenly bodies by
the employment of spectroscopy. It has not only thrown wonderful
light upon the physical and chemical constitution of the sun, fixed
stars, and nebulae, and comets, but it holds out a prospect of
obtaining definite evidence as to the nature of our so-called
elementary bodies.

[Sidenote: its relation to geology.]

The application of the generalisations of thermotics to the problem of
the duration of the earth, and of deductions fr