Cuar. IV,, § 1.] 
considerable proper motion of an otherwise un- 
conspicuous star, first reduced Galileo’s theory to 
successful practice. The details of this elaborate in- 
vestigation have been considered by competent judges 
as among the happiest specimens of astronomical in- 
duction ; and like Professor Henderson’s, they have 
also had the advantage of subsequent and still more 
independent corroboration. Professor Johnson of 
Oxford, using, like Bessel, a divided object-glass 
micrometer (or heliometer, as it is not very appro- 
priately called, never being applied to the sun), has 
obtained results for the parallax of a Cygni almost 
identical with Bessel’s, which was 0°35 of a second. 
I am sorry that my limits will not allow me to 
explain more particularly the details of Bessel’s 
MECHANICS.— WATT. 
865 
method,-which, however, may be found in several 
modern works on astronomy. 
M. Peters of the Observatory of Pulkowa has an-  (311.) 
nounced several additional parallaxes, all determined ™- Peters. 
with the aid of a meridian instrument. He has even 
attempted to infer the mean parallax of stars of the 
Ist, 2d, &c. magnitudes, which M. Struve has com- 
pared with his estimate of relative distance derived 
from other considerations ; but the numbers of as- 
certained parallaxes, as well as their amount, are too 
small, and the anomalies still too apparent (as in 
the case of the star No. 1830 of Groombridge’s 
Catalogue), and the parallactic distances too often 
inverted on the scale of brightness, to allow us to 
attach much importance to these generalizations, 
CHAPTER IV. 
MECHANICS OF SOLID AND FLUID BODIES, CIVIL ENGINEERING, AND ACOUSTICS. 
§ 1. WatT.—Condition of Practical Mechanics previous to the time of Watt. His genius for the 
application of Science to Practice. His successive Improvements on the Steam-Engine. Steam 
Navigation. 
(312.) James Warr may be considered as the most dis- 
James tinguished practical man of science of the last cen- 
wee tury, or even for a much longer period, But this is 
not all, Few men achieve such a reputation as his 
without having done more than originate a great in- 
vention for the use and benefit of mankind in all ages : 
—He also taught men to raise the useful arts to a new 
dignity,—to marry them to genuine, unpretending, 
and inductive science,—to disparage ignorance and 
empiricism, and to render the labours of the work- 
shop subservient to intellectual progress, 
(313.) T have attempted, in the first chapter of this Dis- 
pete sertation, to place the scientific part of engineering in 
Riccing to its due relation to pure physics, and I have compared 
physics. therelation between them to that subsisting between 
Mathematies and Physies—the one as an instrument, 
the other as an end. Now it was this, in particular, 
which made Watt the important character he really 
was, He broughtout the dependence of theformer sub- 
jects, as Newton and others had successfully taught 
and demonstrated that of the latter. 
(314.) To appreciate Watt's merit, we must compare the 
State of purely mechanical contrivances of the period preced- 
area - aa ing the date of his improvements on the steam-engine 
seven- | With those of a similar space of time succeeding it. 
teenth cen- Tn the former we find multitudes of contrivances on 
heat paper—ingenious, indeed, but many of which could 
not be executed ; the greater part of the remainder 
could not be carried into effect through want of know- 
ledge in the inventor. We have large promises of 
VoL. I. 
“ semi-omnipotent engines,” perpetual motions, 
“ quintessences of motion,” and the like, mingled 
with trivial mechanical toys ; or we have elaborate 
diagrams of mill-gearing, lathes, fountains, and saw- 
ing machines without end, illustrated with showy and 
expensive plates, but destitute, for the most part, of 
the slightest novelty of principle, or truly mechani- 
cal skill in application. Here and there, no doubt, 
elegant and appropriate contrivances for communi- 
cating or sustaining motion occur; but nearly all 
the best forms of elementary machinery were of re- 
mote antiquity, excepting those connected with clock- 
work, which, including the great and truly scientific 
application ‘of the principle of Isochronism, formed 
the only considerable step in philosophical mechanics 
for very many years previous to the conception of 
the steam-engine. The statical part of mechanics 
had made more progress, Masonry and Carpentry 
had attained a degree of perfection in many respects 
admirable, under the Italian and Norman architects ; 
but the really difficult theory of machinery in motion 
was little understood before Watt’s day, and the 
knowledge which then existed was unassociated with 
practical skill or commercial enterprize. It could 
be found only in profound treatises of theoretical 
mechanics, and in experimental courses of natural 
philosophy. The sources of power were almost ex- 
clusively those derived from simple gravity and the 
impact of fluids, It was not, indeed, the good for- 
tune of Watt to be the first to employ the admirable 
5R 
