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DEPECTS OF SAVERY'S ENGINE. 141 was 'generally the case; for, to whatever height Savery could raise the water by the direct pressure of the steam, the action of the atmosphere was limited to raising it to twenty or twenty-one feet, before he began to force it.
In addition to these drawbacks was that of depending on the attendant for opening and shutting the cocks at the proper period. This was a fruitful source of accident, and consequently of expense, keeping its great danger out of the question; there being no contrivance, or mechanism to guard against the accumulation of steam, or prevent the risk of accident from an explosion of the boiler. It may be remarked, however, that as the boilers and pipes were usually made of copper, this, in a degree, was somewhat lessened. At this period, also, it was seldom that the engine could be used, with safety, to raise water beyond the height of thirty or forty feet, from an inability of making all the parts of a strength and solidity, which they seldom had the means of doing, and certainly not of ascertaining the fact when it was done.
It was not surprising, therefore, that these imperfections should have materially retarded the introduction of Savery's engine ; nor that they should have furnished occasion to the malicious, or interested to exaggerate its imperfections, and magnify its dangers. The latter, however, seems to have been the greatest drawback on its utility; for many of the mines, which were still productive, were so deluged with water, that to extract it was so far beyond the limit of animal power, that even had steam been a much more expensive power, it must have been resorted to, had further operations been continued. It is not quite clear whetlier Savery introduced them into any of 142 ACCIDENT FROM BURSTING, , the mines, or what was his general arrangement of the apparatus when he used it to pump water from depths exceeding the height of the atmospheric column. In the “ Miner's Friend," he suggests a series of engines, where the mines were deep, placed at the height of sixty feet from each other; thus forcing the water only to the mom derate height of forty or fifty feet, by which means the temperature of the steam could seldom exceed 216° or 220°. In particular cases, this was some. times departed from. Desaguliers states, that he has known engines, erected by Savery long after this period, at work, when the steam was of that heat as to melt soft solder; and he also relates the particulars of an accident, which the use of it at this heat occasioned. But on the whole, considering the uncontroulable power of the agent, which may, at this time, be cousidered as being tirst called into action, the matter for wonder is, not that such casualties might happen, or did hapa pen, but that in so short a time the powers of steam should bave been applied in a manner producing so few disasters; and that too, in a state of the apparatus, in which, excepting mere strength of parts, there was no provision made for safety, or contrivances to allow the steam to escape, when it accumulated to a dangerous limit in the engine,
The project of procuring motion by the fall of a piston into a vacuum was among the earliest to which the experiments with the air-pump gave rise ; and vapour was vow shown to possess properties, by the medium of which this idea might probably be carried into execution. There was but one opinion with regard to the extent and convertibility of the power which might thus be created. Its regular, precise, and economical
143 production was the problem presented for solution to the ingenuity of practical mechanics.
In reviewing the experiments which had been made in the attempt to accomplish this grand object, it is not a little remarkable, that notwithstanding the important purposes to which its application had been suggested, so little was done towards perfecting what may be called the preliminary mechanisi by persons familiar with the projects and labours of their predecessors on this subject, and who themselves were ranked as mechanics of the highest order for forecast and invention. Dr. Hooke, one of the most ingenious and persevering mechanics that England ever produced, must especially be noticed as having evinced à surprising apathy to every thing connected with this machine. He was in the prime of life when the Vauxhall engine was in being; he knew of Papin's schemes described in the “ Acta Eruditorum;" and he also knew of the fine improvement' suggested in the “ Recueil," (1695,) if the fact may be inferred from this book being in his library; and he could not have been ignorant of Savery's labours, in combining a mechanism to employ vapour in a different manner; yet in a letter, of which some extracts are preserved among his papers in the library of the Royal Society, the prepossession he had throughout shown against the first Marpurg schemes appears to have influenced a hasty decision also against the last; for he dissuades an individual, who had applied to him for advice on some project for producing a first mover on this principle, from proceeding further in his experiments, as the idea was grounded on a fallacy:
Of Thomas Newcomen, the person to whom that advice was addressed, and whose name and
labours will henceforward occupy a prominent station in the history of the improvement of the steam-engine, nothing is known beyond a few particulars incidentally furnished by Desaguliers, when describing his inventions. All that can be gleaned from this source is, that he was a blacksmith, residing in the town of Dartmouth, in Devonshire; and the unimportant fact, that he was a member of a religious sect, differing in some points of ecclesiastical discipline from the na-, tional church, and on that account forming a sepa-, rate communion under the denomination of Baptists. The place and time of his birth and death are alike unknown; and after the lapse of a century it were vain to hope to gratify a laudable curiosity, by rescuing even a single traditionary anecdote, either of his habits or acquirements, from oblivion. From the respectful manner however in which Dr. Allen raentions “his very good friend, the ever-memorable Mr. Newcomen, whose death he very much regretted," we may conclude that he enjoyed that rank in society, and regard of men of merit, which his admirable inventions gave him so strong a claim to; and of his colleague and townsman, John Cawley, all that is known of his history is, “that he made provision for the day that was passing over him by following the occupation of a glazier; his labours, whatever they were, have never been discriminated from those of Newco
Dr. Hooke's letter to Newcomen, which has been stated as dissuading him from wasting his time and labour in any attempt to produce motion on Papin's plan, contains a very remarkable expression; remarkable, as showing his total ignorance of the rapidity with which steam was condensed by contact with a cold body. “Could he,
145 (meaning Papin), make a speedy vacuum under your piston, your work is done."
This discouraging opinion, though given by so great a mechanic, had not the effect of damping the ardour of Newcomen and Cawley; for the next time we hear of them is as having followed out the idea of producing a first motion by the fall of a piston into a vacuum made by means of steam, a scheme discarded by Hooke for being surrounded with almost insuperable difficulties.
The rough experiment differed little from that made many years before; but a slight deviation in their apparatus opened a path to the Dartmouth mechanics, which their predecessor had either overlooked or disregarded.
On a cursory inspection, this experiment varies not from Papin's*; the leading idea is unquestionably the same, yet the application and the result are totally different. In the Marpurg cylinder, the steam raised the piston; the vapour, therefore, required to be of a temperature considerably above that necessary to balance the atmospheric column. The substitution of a lever for the rack and wheel, or for the axle and ropes, was not only more convenient, but much simpler; and to the facility of raising the piston by a counterpoise, which this arrangement presented, may have been owing the disuse of high-pressure steam in Newcomen's future experiments.
This will be better understood by a reference to the diagram. The steam generated in a boiler, distinct from the cylinder, permitted these vessels to be placed permanently in the most convenient position. The piston, fixed to a rod, was attached by a joint or chain to the end of a lever, vibrat
P. 92, chap. ii.