26. The sum of the quantities in the eighth column divided by the number of experiments gives 945-03° as the average; but if the second and eleventh experiments, which yield results much smaller than the others, and which Mr. Watt therefore considered objectionable, be omitted, the average will be 949.9°. As several circumstances however affect these experiments, tending for the most part to make the latent heat appear rather less than it actually is, Mr. Watt considers that we shall not err in excess by calling it 960°. 27. One of the circumstances productive of the error above alluded to is the progressive increase or diminution of caloric by radiation, and by the contact of the surrounding atmosphere. This interference with his conclusions, neglected by Mr. Watt, was avoided in a very ingenious and satisfactory manner by count Rumford. At the commencement of his experiment, he rendered the temperature of his apparatus 10° or 12° lower than that of the surrounding air; and the vapor was then allowed to pass into the tube of the refrigeratory. Whilst the temperature of the water around the tube continued below that of the air and adjacent bodies, caloric flowed into it, and it was consequently warmed by them. But the contrary effect occurred, of course, when the circumstances as to temperature were reversed; the surrounding bodies being warmed by the apparatus. Conducting his experiment therefore in such manner that the same time was or cupied in each case, a compensation was obtained, the same quantity of caloric being retained by the whole apparatus as if no portion had been either absorbed or emitted. It is to this ingeni ous precaution, chiefly, that Biot is disposed to ascribe the superior accuracy of Rumford's experiments; and the agreement of their results with those of the profound investigator, Gay Lussac. 28. We have already intimated that the experimental results of Watt and Southern very nearly coincide. Mr. Southern's experiments were performed in 1803 with the intention of ascertaining the latent heat of steam under 3° of elasticity, viz. equal to the support of forty, eighty, and 120 inches of mercury. The following are the results brought into a tabular form :— 1 29. From the above experiments may be calculated the latent heat of the steam formed in each. For, if the weight of the water which received the heat be multiplied by the number of degrees of temperature communicated to it, and the product be divided by the accession of weight to the water, the quotient will give the caloric which the steam lost. By adding to this the temperature of the water in the vessel at the conclusion of the experiment, a number will be obtained showing the whole heat, or the sum of the sensible and latent heat of the steam. Hence, by subtracting the sensible heat of the steam from this sum, the latent heat will be found. Thus latent heat will be 1119°, 1190°, and 1228 and the latent heat 890°, 920°, and 933°. It was distinctly observed, however, that the tin vessel in which the steam was generated imparted heat to the surrounding air: and an experiment was made to determine the amount of this loss. It was found that, when the contained water was at 80°, 1° was lost in five minutes; and, when at 60°, 1° was lost in ten minutes and a-half; it would therefore, probably, lose 1° in eight minutes during the time of performing an experiment-the mean temperature being about 65°. As the excesss of temperature at the be ginning and end of each experiment above that of the air was nearly the same in all, the loss would be nearly proportional to the duration of each hence, to the acquired heat should be added, in the first experiment, 18°; in the second, and in the third; being severally proportional to the said duration. These being respectively added to the temperatures, in cols. t temperature of warm water, and and 6, give in the former 81°, 82°, and 814; rsum of the sensible and latent heat of the and in the latter 33, 34°, and 334°; and if col. 3 x col. 6 col. 5 the sum of the sen ture, w accession of water by the condensed steam, either of these sets of numbers be used in the calculation, according as one or the other of the equations is adopted to develope the results, they will be found to be 1171°, 1212°, and 1245°, for the sums of the sensible' and latent heat; and consequently the latent heat in each experiment will be 9420, 942°, and 950°. 31. From all the experiments to determine the quantity of heat latent in steam, notwithstanding their partial disagreement, it is evident that though steam produced under the ordinary pressure of the atmosphere does not indicate a higher temperature than boiling water, or about 212°, it does actually contain nearly 1200 thermometric degrees of heat. Steam, therefore, when mixed with six times its weight of water at 32°, will raise its temperature to 212°; and it is on this account employed in several brew-houses, dyeing works, and manufactories where large quantities of hot water are required. Many large buildings are also warmed by steam; and it is very advantageously employed in several drying processes where great heat is required, and where the substances to be heated are liable to combustion. 32. To the latent heat thus existing in water when converted into steam, or to the caloric of vaporization, its elasticity is ascribable. Speculation has been active in endeavouring to show how this property is conferred by caloric, but hitherto without effect. Experiment has been more successful in ascertaining the extent of this elasticity; a subject of great practical importance. Many scientific individuals, as before stated, have directed their attention to this enquiry, and the results of their investigations will be found in the following copious synopsis, commencing at 212° 33. SYNOPSIS of experimental and calculated results on the elasticity of vapor. Temperature. SYNOPSIS, &c.-Continued. Forces in inches of mercury. Robi heit. mur. grade. ment. lation. peri- cula Fahren- Reau- Centi- son, by Dalton, Creigh- Watt, ton, by by ex Taylor, experi- by calcu- By ex- By cal- calcula- peri- By ex- By cal-by expe tion. ment. peri- cula- riment. Ure. Southern. ment. tion. ment. tion. Robi [Fahren- Reau- Centi- son, by by calcu-By ex-By cal.ton, by by ex Dalton, heit. mur. grade. experi lation. ment. Creigh- Watt, peri- cula calcula- perition.' ment. ment. tion. 34. Having, in the preceding paragraphs, fur nished our readers with a series of practical illustrations relative to the formation of elastic vapor, it may now be advisable to proceed with a detailed history of the progress of the steam engine. 35. Among the numerous competitors for the honor of having first suggested steam, as a moving power in mechanics, we must certainly place Hero of Alexandria, Brancas, and the marquis of Worcester in the foremost rank. 36. The simple apparatus suggested by Hero about 2000 years ago may be readily understood by reference to the annexed figure. F represents a caldron in which upright pillar furnished with a point at C, support a moveable hollow ring. This is in the first instance filled with water, and the flame of burning alcohol beneath converts it into steam. The bent tube E performs the same office as that at A in the previous diagram, and the steam entering the air in the direction E A leaves an excess of force tending to make the ring revolve in the opposite direction. 38. The second of these candidates was an Italian philosopher of considerable eminence, and who, in 1629, published a treatise entitled Le Machine, &c., which contained a description of an apparatus for the same purpose. 39. Brancas's revolving apparatus, as will be seen by reference to the following diagram, was still more simple than that contrived by Hero. ÔE 40. A hollow copper and furnace, AEB, representing the head of a negro, and filled with water, was furnished with a small tube C, and is seen to give motion to a float-wheel D, which is impelled by the action of the elastic vapor generated within. The work in which this engine was first described was published in 1629. It is exceedingly rare, and the above diagram is copied from an engraving in the possession of major Colby. 41. A slight examination of the principle upon which this simple apparatus is constructed will show that no very considerable force could have been obtained; as the steam, passing through the atmosphere in its passage to the wheel, must, to a certain extent at least, be converted into water. 42. After the publication of this scheme, which it is probable was never put in practice with any useful effect, nearly thirty years elapsed ere the further consideration of the above important subject was resumed by the marquis of Worcester. The mode of employing steam recommended by the marquis, and which he describes in his Century of Inventions to have completely carried into effect, was entirely different from that of his predecessor; and it is evident that the noble author had received no previous hint of Brancas's invention, as he expressly states, in another part of the above work, that he desired not to set down any other mens' inventions;' and if he had in any case acted on them, to nominate likewise the inventor.' 6 6 43. It is said that the marquis, while confined in the Tower of London, was preparing some food on the fire of his apartment, and the cover, having been closely fitted, was, by the expansion of the steam, suddenly forced off and driven up the chimney. This circumstance, attracting his attention, led him to a train of thought, which terminated in this important discovery. But no figure has been preserved of his invention; nor, as we have good reason to suppose, any description of the machine he employed, except the sixty-eighth article in the above-mentioned work. We shall content ourselves, therefore, with extracting that article from the noble author's MS. preserved in the British Museum. 44. An admirable and most forcible way to drive up water by fire; not by drawing or sucking it upwards, for that must be as the philosophers call it infra sphæram activitatis, which is but at such a distance. But this way hath no boundary, if the vessels be strong enough; for I have taken a piece of a whole cannon, whereof the end was burst, and filled it three-quarters full of water, stopping and screwing up the broken end, as also the touch-hole; and making a constant fire under it, within twenty-four hours it burst, and made a great crack; so that having found a way to make my vessels so that they are strengthened by the force within them, and the one to fill after the other, I have seen the water run like a constant fountain stream, forty feet high; one vessel of water, rarefied by fire, driveth up forty of cold water. And a man that tends the work is but to turn two cocks, that one vessel of water being consumed, another begins to force and refill with cold water, and so successively, the fire being tended and kept constant, which the self-same person may likewise abundantly perform in the interim, between the necessity of turning the said cocks.'-Vide Harleian MSS. No. 2428. 45. In 1683, a scheme for raising water by the agency of steam was offered to the notice of Louis XIV., by an ingenious English mechanic, of the name of Morland. He was presented to the French monarch in 1682, and in the course of the following year his apparatus is said to have been actually exhibited at St. Germain's. The only notice of this plan occurs in the collection of MSS. to which we have already alluded, and forms the latter part of a very beautiful volume, containing about thirty-eight pages, and entitled Elevation des Eaux, par toute sorte de Machines, réduite a la mésure, au poids, et a la balance. Presentée a sa Majesté tres Chrestienne, par le Chevalier Morland, gentilhomme ordinaire de la chambre privée, et maistre des méchaniques du Roy de la Grande Brêtaigne, 1683.' 46. The MS. is written upon vellum, richly illuminated, and the part which has reference to the steam engine occupies only four pages, com mencing with a separate title, &c. It is also accompanied by a table of the sizes of cylinders, and the amount of water to be raised by a given force of steam. This curious memoir forms an important link in the chain of historical evidence which tends to prove that the English, though not the actual inventors of the steam) engine, were unquestionably the first to apply its stupendous powers to any useful practical purpose; we shall, therefore, offer no apology for presenting an entire translation to the notice of the reader. 47. The principles of the new Power of Fire; invented by the Chev. Morland in the year 1682, and presented to his most Christian Majesty, 1683. Water being evaporated by the power of fire, the vapor shortly acquires a greater space (nearly 2000 times) than the water occupied before; and, was it to be always confined, would burst a piece of cannon. But being well-regulated according to the laws of gravity, and reduced by science to measure, to the weight and balance, then they carry their burdens peaceably (like good horses), and thus become of great use to mankind, particularly for the elevation of water. 48. In 1695, Papin, then resident at Cassel, published a work, describing a variety of methods for raising water, in which he enumerates the above invention. Being unable to procure this tract, we insert the following trans |