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engines general topics of conversation, and consequently “ universally known; which they were by no means before in “ this country.” And on the 14th of June, 1785, he took out a patent " for certain newly improved methods of constructing “furnaces or fire-places for heating, boiling, or evaporating " of water and other liquids which are applicable to steam-engines and other purposes, and also for heating,

melting, and smelting of metals and their ores, whereby "greater effects are produced from the fuel, and the smoke is " in a great measure prevented or consumed,” which newly improved methods he describes to consist“ in causing the smoke

or flame of the fresh fuel, in its way to the flues or chimney, " to pass together with a current of fresh air through, over, “ or among fuel which has already ceased to smoke, or which " is converted into coke, charcoal, or cinders, and which is

intensely hot, by which means the smoke and grosser parts “ of the flame, by coming into close contact with, or by “ being brought near unto the said intensely hot fuel, and " by being mixed with the current of fresh or unburnt air, “ are consumed or converted into heat, or into pure flame « free from smoke."

“I put this in practice," he continues,“-“First, by stop"ping up every avenue or passage to the chimney or flues,

except such as are left in the interstices of the fuel, by

placing the fresh fuel above, or nearer to the external air, “than that which is already converted into coke or charcoal ; “and by constructing the fire-places in such manner that the “flame, and the air which animates the fire, must pass down“ wards, or laterally or horizontally, through the burning “ fuel, and pass from the lower part, or internal end or side “ of the fire-place, to the flues or chimney. In some cases, “after the flame has passed through the burning fuel, I “ cause it to pass through a very hot tunnel, flue, or oven, “ before it comes to the bottom of the boiler, or, to the

part of the furnace where it is proposed to melt metal, or

perform other office, by which means the smoke is still “ more effectually consumed. In other cases I cause the “ flame to pass immediately from the fire-place into the space

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“ under a boiler, or into the bed of a melting or other “ furnace.” He varied the figure or form and proportions of the fire-places, &c., but in all cases the principle was the same; the fresh or raw fuel being placed next to the external air, and so that the smoke or flame passed over or through the coked or charred part of the fuel.

Secondly,” he goes on, “in some cases I place the fresh “ fuel on a grate as usual, and beyond that grate, at or near “ the place where the flame passes into the flues or chimneys, “I place another small grate, on which I maintain a fire of "charcoal, coke, or coals which have been previously burnt “ until they have ceased to smoke; which, by giving intense “ heat and admitting some fresh air, consumes the smoke of “ the first fire.

Lastly, be it remembered,” he concludes, “ that my said new invention consists only in the method of consuming the “smoke and increasing the heat, by causing the smoke and “ flame of the fresh fuel to pass through very hot tunnels or

pipes, or among, through, or near fuel which is intensely hot, and which has ceased to smoke, and by mixing it with “ fresh air when in these circumstances; and in the form and “ nature of the fire-places herein mentioned, described, and “ delineated : the boilers and other parts of the furnaces

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being such as are in common use. And be it also remem“ bered, that these new invented fire-places are applicable to “ furnaces for almost every use or purpose.

The Specification, which was enrolled on the 9th of July, 1785, is printed in the • Mechanical Inventions of James Watt,' 1854, vol. iii.

pp. 115 to 121 ; and the relative drawings are engraved on Plates XXX., XXXI., XXXII., and XXXIII., of the same work.

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CHAPTER XX.

HISTORY OF THE DISCOVERY OF THE COMPOSITION OF WATER — MR.

WATT'S STUDY OF CHEMISTRY STATE OF THAT SCIENCE PREVIOUS TO 1783 BLACK AND PRIESTLEY MACQUER VOLTA - WARLTIRE CAVENDISH DREW NO CONCLUSION FROM HIS EXPERIMENTS-LAVOISIER --HIS KNOWLEDGE OF THE EXPERIMENTS OF CAVENDISH, AND OF THE CONCLUSIONS OF WATT.

IN 1783,—one of the busiest of those ten years of his life which may thus be said to have teemed with experiments and inventions,-Mr. Watt had the further honourable distinction of making and publishing his famous discovery of the Composition of Water. It must be added, though we do so with regret, that, as in his greatest mechanical inventions, so in this matter also, he experienced the unpleasant necessity of vindicating his own just claims from the unexpected, and, as we believe, most men will be of opinion, the unjustifiable, interference of others. It was an occasion, however, on which the firmness, moderation, and true greatness of his mind were signally manifested; and the circumstances of which, as displayed in his Correspondence on the subject, have contributed in every way to increase his good name.

His principal inventions connected with the steam-engine, with all their prodigious results, were founded, as we have seen, on the attentive observation of great philosophical truths; and the economy of fuel, increase of productive power, and saving of animal labour, which gradually ensued, all originated in the sagacious and careful thought with which he investigated the nature and properties of heat. The department of physical science with which, next to mechanics, he may be said to have been at one time most familiar, and which long continued to occupy some of his leisure hours, was Chemistry. With what success he studied it, we know from the testimony of the most eminent

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among his contemporaries who directed their attention especially to that subject, and many of whom were his frequent correspondents. “He was equally distinguished," said the late illustrious President of the Royal Society, Sir Humphry Davy, “as a natural philosopher and a chemist, and his “ inventions demonstrate his profound knowledge of those sciences.

."* The numerous experiments which he made with a view to the attainment of the great principles of which he was in search, are further commended by the same accomplished and able judge, as difficult, delicate, and refined.

It is stated in the Memoirs of his friend and neighbour, the celebrated botanist Dr. Withering, that “in his estimation, “Mr. Watt's abilities and acquirements placed him next, if “ not superior, to Newton ;” † a judgment dictated, no doubt, by the kind partiality of a friend, but showing the estimation in which Mr. Watt's talents were held by an able and discerning man of science. How intently he watched the phenomena, how deeply he penetrated into the causes of chemical action, might be conceived from his friend Robison's description of him as "a philosopher in the most exalted sense of “ the word, who never could be satisfied with a conjectural “ knowledge of any subject, and who grudged no labour nor "study to acquire certainty in his researches."The highest merit certainly attaches to his chemical discoveries, and deep interest must be felt by all who attend to the history of their origin and progress, from the fact that he was in this, as in almost every other part of learning, in a great measure selftaught. He has himself, on one of the very few occasions on which he ever made public any of his writings through the medium of the press, (the others being only communications to the Royal Society, which were ordered to be printed,) taken pains to correct the statements of Professor Robison on this point. That gentleman,-misled, perhaps, by Mr. Watt's own expression on hearing of the death of Dr. Black, “he taught me to reason and experiment in natural

* Speech

1824.- Translation of thering, by his Son, 1822. Vol. i. Arago's • Eloge,' p. 191.

+ Tracts and Memoir of Dr. Wi- | Preface to Black's Lectures,

p. 46.

philosophy,”—in dedicating to him his edition of Dr. Black's Lectures, called him Dr. Black's pupil, declared that he had attended two courses of his lectures, and even alluded to his professing to owe his improvements on the steamengine to the instructions he had received from that eminent teacher. This, however, is altogether erroneous; and Mr. Watt has lamented that the necessary avocations of his business at that time prevented his attending either Dr. Black's or any other lectures. But he repeatedly acknowledged the information and pleasure he derived from the conversation of that enlightened philosopher, as well as from the friendship of such men as Robert Simson and Dr. Dick, both distinguished cultivators of kindred branches of natural knowledge.

In establishing himself at Soho, he retained his habits of intimate correspondence with Dr. Black, who had then, for more than twenty years, made known his discovery of carbonic acid gas, and for at least sixteen had annually explained his theory of latent heat in his lectures, in which, also, for the first time, he developed the doctrine of the capacities of bodies for heat, (or that of specific heat); and who, after spending ten years of academical labour in the University of Glasgow, had, in 1766, accepted that professorial chair in Edinburgh, which for thirty years longer he continued to render famous.

* See his Preface to his edition of admirable a discovery. "I began,”. Dr. Robison's Articles, •Steam' and says the Doctor, “ to give the doctrine Steam-Engine,' given in Chapter " of latent heat in my lectures at Xxvii. of this volume.

Glasgow, in the winter 1757-58, + We have much pleasure in being “ which I believe was the first winter able, on indisputable authority, to “ of my lecturing there, or, if I did attribute the public announcement of “not give it that winter, I certainly Dr. Black's theory of latent heat to a gave it in the 1758-59, and I have period considerably earlier than had “ delivered it every year since that formerly been named, even by Dr. “ time in my winter lectures, which I Black’s zealous admirer and pupil, “ continued to give at Glasgow until Lord Brougham. His Lordship says “ winter 1766-67, when I began to that Dr. Black meditated on that “ lecture in Edinburgh.” theory, investigated it by experiment, In the same letter he mentions by and taught it in his lectures, at least name many distinguished foreigners, as early as 1763. But the following as well as natives of this country, extract from his letter to Mr. Watt, of who had attended some of the earliest 15th March, 1780, furnishes informa- courses of his lectures, and had then tion more precise, and assigns with heard his explanations of that recertainty a much earlier date to so markable theory; adding, that about,

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