800 MATHEMATICAL AND PHYSICAL SCIENCE. [Diss. VI. 
the former part of the statement ; and when we recol- 
lect that the same period has given birth to the steam- 
engine of Watt, with its application to shipping and 
railways,—to the gigantic telescopes of Herschel and 
Lord Rosse, wonderful as works of art as well as in- 
struments of sublime discovery,—to the electric tele- 
graph, and to the tubular bridge,—we shall be ready 
to grant the last part of the proposition, that science 
and art have been more indissolubly united than at 
any previous period. 
(6.) The Dissertation of Professor Playfair closes with 
Limits of the period of Newton; that of Sir John Leslie, pro- 
a “fessedly deyoted to the history of the eighteenth cen- 
tury, embraces some matters which belong more 
properly to those which preceded and followed it. 
After considering how I might best carry out the plan 
of these essays, I have adopted the period from about 
the year 1775 to 1850 as the general limit of my 
review. We may imagine this period, of three quar- 
ters of a century preceding the present time, to be 
divided into three lesser intervals of 25 years each, 
which have also some peculiar features of their own. 
(7.) From 1775 to 1800 many branches of science still 
ane continued in the comparatively inert state which cha- 
of the 18th T2cterized a great part of the eighteenth century. 
century. There were, however, two or three notable excep- 
tions. One was the continued successful solution of 
the outstanding difficulties of the Theory of Gravity 
applied to the moon and planets, a task in which the 
continental mathematicians, and of these, in chief, 
Lagrange and Laplace, had no rivals, or even coad- 
jutors, on this side of the channel: Another was the 
foundation of Sidereal Astronomy by Sir William 
Herschel ; and the last was the commencement of a 
system of Chemical Philosophy based on new and im- 
portant experiments, and including the laws of heat 
in combination with matter, which at that period very 
naturally ranged themselves within the province of 
the chemist. In this department two British and 
one foreign name stand conspicuous, Black, Caven- 
dish, and Lavoisier. I do not of course mean to affirm 
that other branches of science were not cultivated 
with success within’the exact period of which we 
speak. Electricity, for instance, first statical, after- 
wards that of the pile, had a share in the discoveries 
and speculations of the time. But these were rather 
themere extension of what had previously been thought 
of; or the first dawn of future important results, whose 
development fills a large space in the succeeding story. 
Volta and his inventions belong rather to the nine- 
teenth than to the eighteenth century. 
(8.) The first quarter of the present century attained 
Character a higher and more universal celebrity. Scarcely a 
vars branch of physical science but received important 
1900-1925, and even capital additions. Physical Astronomy in- 
deed, no longer filled so large a space in the page of 
discovery, simply because the exhaustive labours of 
the geometers of the former period had brought it to 
a stage of perfection nearly co-ordinate with the means 
of observation, and because, by the publication of the 
Mécanique Céleste, Laplace had rendered available M 
and precise the masses of scattered research accu- 
mulated by the labours of a century since the close 
of Newton’s career of discovery. It was in some 
sense a new book of “ Principia,”—not, indeed, 
the work of one, but of many; nor of a few years, 
but of two generations at least. Still there it was, 
a great monument of successful toil, which, like its 
prototype, was for many years to be studied, even by 
minds of the highest order, rather than to be enlarged. 
But the other branches of Natural Philosophy 
were now to make a stride, such as perhaps no pre- Experi- 
ceding time had witnessed. The science of Optics 
was speedily expanded almost twofold, both in its 
facts and in its doctrines. Galvanic Electricity dis- 
closed a series of phenomena not less brilliant and 
unexpected in themselves than important from the new 
light they threw on the still dawning science of che- 
mistry, and from the power of the tool which they 
placed in the hands of philosophers. Before the 
first quarter of the present century closed, the import- 
ant and long suspected connection between Electricity 
and Magnetism was revealed, and its immediate con- + 
sequences had been traced out with almost unpa- 
ralleled ingenuity and expedition. The basis of the 
science of Radiant Heat, slightly anticipated by the 
philosophers of the eighteenth and even the seven- 
teenth centuries (Lambert and Mariotte), was finally 
laid in a distinct form, assigning to the agent, heat, 
an independent position dissociated from grosser 
matter, such as light had long enjoyed. Astronomy, 
though enriched on the very first night of the new 
century by the discovery of a small planet, the he- 
rald of so many more of the same class, made per- 
haps less signal progress ; but Chemistry, besides the 
aid it received from the invention of the pile, had a 
triumph peculiarly its own in the addition of the 
comprehensive doctrine of Definite Proportions, des- 
tined to throw at some later time a steady light on 
the vexed question of the constitution of matter. 
The great number of scientific names of the first or- 
der of merit concerned in these numerous discoveries 
marks the extraordinary fertility of the period. They 
are imperfectly comprehended in the following list : 
Young, Malus, Sir David Brewster, Fresnel, and 
Arago ; Volta, Dalton, Davy, and Oersted ; Prevost, 
Leslie, and Fourier; Gauss, Ivory, Olbers, Bessel, 
and Encke. 
' Of the twenty-five years just elapsed, it is not so 
easy to speak with precision. The voice of criticism Period 
may be fairly uttered with that reserve which every 
one must feel in speaking of his immediate contem- 
poraries. Yet it may perhaps be stated without 
just cause either of offence or regret, that it has not 
on the whole been characterized by the full maturity 
of so many commanding minds. Of the great dis- 
coverers of the former period, several survived and 
continued their efficient labours during no small por- 
