CHAP. IV., 1.] 



MECHANICS. WATT. 



71 



by the inertia of the moving machinery, but chiefly 

 by the continuous though constantly diminishing 

 elasticity of the steam as it expands and fills the en- 

 tire cylinder. 1 It is evident that, in the extreme case, 

 the work required (in pumping) will be accomplished 

 if the piston reach the end of the stroke just as its 

 momentum is exhausted, and that, on the other hand, 

 if the pressure of the steam remain constant through- 

 out, the velocity will be a maximum just when the 

 work being done by the machine is suddenly com- 

 pleted, and so much moving power will be wasted. 

 A medium distribution produces the most favourable 

 result in practice, and it depends entirely upon the 

 ratio between the resistance and the effective pres- 

 sure of the steam what this most favourable propor- 

 tion will be. In the single-pumping engines of Corn- 

 wall, in which the economy of fuel is carried to the 

 highest perfection, it frequently happens that not 

 more than one-eighth of the stroke is performed un- 

 der the full pressure of the steam, which acts expan- 

 sively during the remainder of the stroke ; but these 

 engines, though condensing, are moved by steam of 

 four times the elasticity of the atmosphere. The 

 Cornish engines have been very elaborately perfected, 

 and they have been more carefully tested in respect 

 to performance than any others. It is perhaps not 

 too much to say that they do not contain a single 

 contrivance of any importance (beyond of course 

 what they have in common with the atmospheric 

 engine), which was not the unaided invention of Mr 

 Watt. 



In the Cornish engine we see the Energy of Heat 

 rendered available to an extent which the inventor 

 himself would at one time have thought scarcely cre- 

 dible. The combustion of a bushel of coal which in 

 a Newcomen's engine improved by Smeaton was 

 capable of raising 3,000,000 pounds through one 

 foot, in Watt's improved pumping engine raised 

 20,000,000 pounds the same height. But by the 

 indefatigable skill and perseverance of engineers the 

 Cornish pumps now yield at least Jive times the last 

 amount. This, however, is not the place to enter 

 upon these details, nor can we stop to particularize 

 the other and various mechanical inventions intro- 

 duced by Watt in the form of valves, governors, and 

 steam-indicators. Still less can we enlarge upon the 

 endless and still multiplying applications of this ad- 

 mirable moving power, which is as capable of super- 

 seding the greatest natural forces hitherto applied by 

 man to the useful arts, as it is adapted by its easy 

 regulation to replace human industry in the most 

 delicate operations ; " the trunk of an elephant, 

 which can pick up a pin or rend an oak, is as nothing 

 to it.'" 



Of the applications of the steam-engine with which (325.) 

 Mr Watt was less immediately connected, its adap- , . PP ^ a " 



* i_* i i tion or 



tation to locomotion in the case ot ships in the last steam to 

 century, and in that of railway trains in the present, navigation. 

 have been the most striking, and fraught with con- 

 sequences the most important to mankind. Of the 

 latter we shall have occasion to speak in a future 

 section ; of the origin of steam navigation we may 

 here say a very few words. Passing over projects 

 which never were realized, of moving barges by steam, 

 or other inanimate power, against wind and tide, 

 such as those of Worcester, Papin, and Hulls, we 

 find that the first experiment entitled to be called 



successful was made by Mr Miller of Dalswinton in Miller 



Scotland, conjointly with Mr James Taylor, tutor in Taylor, 

 his family, who together formed the project of mov- 

 ing vessels by means of paddle-wheels driven by a 

 steam-engine, and realized it with the aid of Sym- 

 ington, a practical engineer. As we shall also find 

 in the case of steam-carriages, the Idea of the applica- 

 tion of the steam-engine to move ships was already 

 a familiar one to the minds of many persons about 

 the middle of the last century. To put it in practice 

 with advantage was the step required. Mr Miller's 

 first boat was launched on Dalswinton Loch in Dum- 

 friesshire, in October 1788, and attained a speed of 

 five miles an hour. The subject was pursued by 

 Symington and others. In 1789 a larger vessel was 

 propelled on the Forth and Clyde Canal. Subse- 

 quently, however, the invention languished. The 

 want of co-operation, of capital, and ingenuity, na- 

 turally extinguishes many valuable inventions. Watt 

 himself was only rescued from the same difficulty by 

 the unusual intelligence of Boulton and Small, his 

 coadjutors at Birmingham. Symington was less for- 

 tunate, as well as probably less meritorious ; and 

 though it is well established that Fulton, who passes 

 on the other side of the Atlantic for the inventor of 

 steam-ships, had seen the relics of Symington's second 

 experiment, we must do the Americans the justice to 

 say that the application of steam to navigation first 

 flourished in the United States. In 1807 Fulton Fulton, 

 started a river boat with an engine of Boulton and 

 Watt. In 1813 the example was tardily imitated on 

 the Firth of Clyde. The subsequent improvements 

 need not here be specified. They have been very 

 great and striking, but with the exception of the recent 

 substitution of the screw-propeller for paddle-wheels, 

 they scarcely involve any new principles. 3 



We may briefly close what we have to say of Mr (326.) 

 Watt personally. His health was feeble from child- *JjJJJj, 

 hood, but being blessed with much calmness of tern- O f \y att . 

 per he prolonged his life to a great age, and passed 

 through its struggles, though they were to him con- 



le-acting engine was planned in 1774 or 1775. The expansion principle was first used in 1776 ; the parallel motion 

 in 1784. Watt's Notes on Dr Robison's Article. Robison's Mech. Phil., vol. ii. 2 Lord Jeffrey. 



1 The double- 

 was patented .. . 



a For farther details on the history of Steam Navigation, see that article in the Encyclopedia ; and Mr Bennet Woodcraft's 

 work on the subject, London, 1848. 



