a series of experiments on the elastic force of the steam of water, and of alcohol, (see art. 95&104;) and we have only here to remark on them, that they were not anade with sufficient accuracy even to establish the justness of some of his own views on the subject; also, the rule for the elastic force of steam derived from these experiments, and stated to be sufficiently exact for practical purposes" is very far from being so, and has had a little effect in misleading some of the engineers who have ventured to speculate on the improvement of steam engines. But, on the whole, Dr. Robison's is the best article on steam I have seen.

66

The article on the steam engine consists of the history, mixed with detailed descriptions, of the engines of Savery, Newcomen, Watt. &c.; and such theoretical discussion as he has given is also blended in the same mass. In the historical portion the memory of Papin is not quite so respectfully treated as we could have wished, and the circumstance of Watt being the private friend and countryman of the author has not been without its effect on the historian. In other respects Dr. Robison has been impartial. In description there is a want of system, but he is full and particular; and he has been of unknown value in giving information to the competitors of Boulton and Watt, and in furnishing matter for minor writers. In theory he has reprinted the speculations of Bossut respecting the best velocity for atmospheric engines, with some additions, and Watt's mode of computing the pressure on the piston of the expansive engine; but neither of these inquiries are conducted in such a manner as to be of use to engine makers.

The reputation of Dr. Robison has given much additional value to his articles on the steam engine; hence their effect has been unparalleled, and if we find little of novelty in his labours, it was no small favour to have the scattered knowledge on the subject collected with so much skill, and treated with so much clearness and good taste.

51.—A modification of Watt's manner of constructing boiler fire places was contrived in 1800, by Messrs. Roberton, of Glasgow, which is more convenient in practice though the same in principle. (See Sect. III.) They also attempted to make the steam which escapes by the sides of pistons useful in adding to the effective power of engines. But the complexity and expense of apparatus to obtain so small an increase of power, renders this and some other expedients of that time of little if any value.

1801. Joseph Bramah, born 1749, died 1814.

52.-The rotary engine, the joint product of Messrs. Bramah and Dickinson, has already been noticed, (art. 39.) In 1801 Mr. Bramah obtained a patent for a new mode of applying the four-passaged cock to steam engines, with some other variations in their con

struction.

The four-passaged coek he made to turn continually in the same direction, and yet

produce the same effect as by turning it backwards and forwards, but by turning constantly the same way the wear is rendered more equable, and consequently the combination is more durable.

He also adjusted the movements so as to give, at the proper time, as instantaneous and free a passage to the cylinder and condenser as possible; and formed the apertures so that the cone might be pressed equally into its seat by the force of the steam.

The mining and manufacturing interests of the country felt most severely the injurious effect of the exclusive privileges that had been granted to Boulton and Watt, without those restrictions which ought to guard public rights when a power of monopoly is renewed; and their claims to those privileges were strongly contended against, and the imperfections of their specification exposed with enthusiastic warmth, by Mr. Bramah, in a pamphlet published in 1797. Indeed the fortunate idea of condensing in a separate vessel, which in Watt's single engine is the only essential part in saving of fuel beyond what Smeaton had accomplished, would undoubtedly in a short time have occurred to some other person, and mines must have been drained at a more economical rate, long before that monopoly ceased. The progress of the public good should never be retarded for individual interest, and therefore monopoly should never be renewed except so that any other person may, at a fair and at a fixed rate of licence, join in it.

53.-A series of tables for the proportions of the cylinders of atmospheric engines, to produce a given effect, were published, in 1801, by Mr. Thomas Fenwick, whose employment in the management of coal works near Newcastle gave him a good opportunity of knowing what would answer best in practice.

He infers from some experiments that the whole friction of the atmospheric engine is about four pounds per square inch, on the area of the piston, and on account of the frequent bad effects attending designing an engine with too small an allowance for excess above its ordinary work, he makes his computations at five pounds and a half effective power for each square inch of piston.

In a later edition of his work he gives tables for an improved atmospheric engine with a separate condenser in which the ratio of the effect is as 17: 10, when the same sized cylinder is used. The saving of fuel he does not mention, as at coal works it is not considered of much importance; for if the first expense of an engine be small, and its operation simple and efficient, it is of more value to a coal owner than a finer piece of machinery.

1801. John Dalton.

54. At this period a knowledge of the nature and properties of vapours began to become important in chemical science, in meteorology, and in other branches of natural philo

sophy, and therefore a wholly different class of writers engaged in the investigation, which had made so little progress in the hands of mechanical people. The first chemist who distinguished himself by attempting a full investigation of the theory of vapour was Mr. John Dalton. He made an accurate series of experiments on the expansive force of steam at temperatures lower than 212o,-made experiments and ascertained various phenomena relative to the expansion of gases, the mixture of air and vapour, the nature of evaporation and of combustion. And though he failed in his attempt to reduce any of these to general laws, yet he gave such an impulse to the inquiry as rendered it one of universal research among chemical philosophers. The importance of Dalton's inquiries, and even their connection with the theory of the steam engine, did not appear, at first, to be much noticed. The idea that Watt had done every thing possible to be done respecting the power of steam had stopped inquiry among men of science, and left the manufacturers and capitalists of the country, who were wishful to encourage improvement, to be guided by vain and ignorant projectors, or ruined by pretending knavery.

55.-In 1801, Mr. Symington was encouraged to proceed with a steam boat, by Thomas, Lord Dundas, of Kerse, who wished that one might be applied to drag vessels on the Forth and Clyde Canal in place of horses, and accordingly a series of experiments on a large scale, which cost nearly £3000; were set on foot in the year 1801, and ending in 1802 The boat Mr. Symington made was for towing, and it had a steam cylinder twenty-two inches in diameter, and four feet stroke. A complete model of it, with a set of ice-breakers attached, may be seen at the rooms of the Royal Institution in London. This tow-boat proved to be very much adapted for the intended purpose, but no direct practical application of steam power to this object resulted from it.

56.—The idea of a high pressure engine had occurred to Leupold, (art. 12.) and to Watt, (art. 26.) but neither of them had reduced their notions to practice, and it was not till 1802 that this simple mode of applying steam was brought into use by Messrs. Trevithick and Vivian.* Their object seems to have been to form a simple and portable engine for cases where water was scarce, or where gaining the whole effect of the fuel was of less consequence than moving a cumbrous load of matter.

Indeed their high pressure engines were intended chiefly for propelling of carriages upon rail-roads, and when used for this purpose the boiler was composed of cast iron, of a cylindrical form; mounted horizontally upon a frame with four wheels, the cylinder of the engine being placed vertically within the boiler near to one end. The piston rod moved a cross head, between two guides, and by a connecting rod descending from each end of the cross head to two cranks the motion was communicated to the wheels of a carriage; a fly wheel in this case is not required because the momentum of the carriage supplies its place.

The first trial of this species of moving power for carriages took place on a railway at Merthyr Tidvil in 1805. Its use was not at that period followed up, but it is now with some slight modifications extensively employed on rail-roads.

Several projects for trifling variations in the construction of engines, and for methods of applying fuel, appeared about this time, but none of either sufficient novelty or importance to claim particular attention.

The nature and application of heat had been so well illustrated by Rumford, and many of its more recondite properties so ably developed by Leslie, that there seemed to be little reason to expect any material improvement beyond the best mode then in practice. The cylindrical boilers which Blakey projected, and Rumford had tried, were again remodelled by Woolf; but in his practice we find he has reverted to methods nearly like those of Rumford, instead of continuing to follow his own. The steam engine itself had also apparently obtained its most simple and efficient form, except in the eyes of those who expected to use its direct rotary action. The fact however was otherwise, for by a most simple change of a previous combination it had to be materially improved.

57.-The mode of condensation invented by Watt being now public property, and the term of Hornblower's patent having expired, Mr. Woolf adopted the arrangement of the latter, with the alteration of using high pressure steam in the small cylinder, and employing the condensing apparatus of Watt. But a change of the working force of the steam would have been too slight a ground to have claimed a patent upon, and therefore he commences his specification with a claim of the discovery of a new law of the expansibility of steam. This law of expansibility he stated, with much confidence, as the result of experiments; but no doubt he had deceived himself. His assumed law of expansion, is, that steam generated at any number of pounds above the pressure of the atmosphere will expand to an equal number of times its volume, and still be equal in elastic force to the pressure of the atmosphere, the temperature being unaltered. Hence steam generated at forty pounds on the square inch was expected to expand to forty times its bulk, and yet be

equal to the elastic force of the atmosphere. But it is a well known law of the expansion of fluids that the temperature being constant, the bulk is inversely as the pressure; and calling the pressure of the atmosphere fourteen pounds, we have 14: 14+40 :: 1: 4, nearly. Therefore steam generated at fifty-four pounds on the square inch, or forty pounds above the pressure of the atmosphere, would expand only to four instead of forty times its volume. (See art. 120.) And though Woolf's assertions were so directly opposed to the laws of the constitution of elastic fluids, they have found their way as undoubted experimental truths into works which ought to have high claims to respectability; and it should be a lesson of care to authors, unless they have no higher wish than to reprint advertisements.

The employment of high pressure steam to act expansively by means of a double cylinder, gives the utmost degree of power in the most equable manner, and with the most safety. Hence either for machinery engines, or mine engines, it seems the most economical mode of obtaining power. I object to strong steam on account of its danger, but my readers may not have like apprehensions. Woolf's other patents are for projects of little if any value.

58.-It would be an omission to pass without notice the exertions made by Oliver Evans about this period to get into use the high pressure steam engine. His scheme for employing it had not at first many supporters, and he had some rivals. His engine differs little from that of Trevithick and Vivian in construction, but from a work called "The Abortion of the Young Steam Engineer's Guide" it appears, that the expansive force of the steam was to be employed. The "Abortion" is a curious work, it betrays that strange mixture of absurd speculation and indistinct perception of truth, which distinguishes the generality of enthusiastic projectors, and is valuable only to those who can select by means of previous knowledge or experience. A volcanic steam engine, and the idea of employing the force of solar heat by means of a burning glass to work an engine, are among his projects.

59.-The claims of our American brethren to improvement, and to judicious construction and application, are however much stronger than those of our continental neighbours; and of American claims we have reason to speak with pride rather than with other feeling. British genius and industry have not been extinguished by transplanting to another climate. It is true that many of the projects they have yet formed are rather extravagant than novel, being seldom founded on the sober reasoning of science. Time will, however, check this evil, and we may expect them to hold that rank in the new world which Britain has held with such honour for some centuries in the older portion. The chief object of their engineers has been to render steam useful in navigation; and considering the importance to America of navigating her immense rivers, it is not surprising that the application of the power of steam to propelling vessels should by persevering efforts have