CHAP. IV., 1.] 



MECHANICS. WATT. 



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 



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 M - Peter8 

 with the aid of a meridian instrument. He has even 

 attempted to infer the mean parallax of stars of the 

 1st, 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 

 Watt. 



(313.) 

 Relation 

 of engi- 

 neering to 

 physics. 



(314.) 

 State of 

 mechanics 

 in the 

 seven- 

 teenth cen 

 tury. 



JAMES WATT may be considered as the most dis- 

 tinguished practical man of science of the last cen- 

 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. 



I have attempted, in the first chapter of this Dis- 

 sertation, to place the scientific part of engineering in 

 its due relation to pure physics, and I have compared 

 the relation between them to that subsisting between 

 Mathematics and Physics 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 brought out the dependence of the former sub- 

 jects, as Newton and others had successfully taught 

 and demonstrated that of the latter. 



To appreciate Watt's merit, we must compare the 

 purely mechanical contrivances of the period preced- 

 ing the date of his improvements on the steam-engine 

 with those of a similar space of time succeeding it. 

 In the former we find multitudes of contrivances on 

 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 



" 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 



