sible, and the vacuum the most perfect, it was necessary that the cylinder should condense no steam on filling it, and that, when condensed, the water, forming the steam, should be cooled down to 100 degrees, or lower. In reflecting on this desideratum, he was not long in finding that the cylinder must be preserved always as hot as the steam that enters it; and that, by opening a communication between this hot cylinder when filled with steam, and another vessel exhausted of air, the steam, being an elastic fluid, would rush into it, until an equilibrium was established between the two vessels; and that if cold water, in sufficient quantity, were injected into the second vessel, the steam it contained would be reduced to water, and no more steam would enter until the whole was condensed.

"But a difficulty arose-How was this condensed steam and water to be got out of the second vessel without letting in air? Two methods presented themselves. One was, to join to this second vessel (which, after him, we shall call the condenser) a pipe, which should extend downwards more than 34 feet perpendicular, so that the column of water contained in it, exceeding the weight of the atmosphere, would run out by its own gravity, and leave the condenser in a state of exhaustion, except in so far as the air, which might enter with the steam and injection water, should tend to render the exhaustion less perfect: this air he proposed to extract by means of a pump. The second method which occurred, was to extract both air and water by means of a pump or pumps; which would possess the advantage over the other, of being applicable in all situations. This latter contrivance was therefore preferred; and is known by the common name of the Air-pump. There still remained some defects unremedied in Newcomen's cylinder. The piston in that engine was kept tight by water; much of which passing by the sides, injured the va

cuum below, by its evaporation; and this water, as well as the atmosphere which came into contact with the upper part of the piston and sides of the cylinder at every stroke, tended materially to cool that vessel. Mr Watt removed these defects, by applying oils, wax, and fat of animals, to lubricate his piston and keep it tight; he put a cover on his cylinder (with a hole in it, made air and steam tight, for the piston-rod to pass through), and employed the elastic force of steam to press upon the piston: he also surrounded the cylinder with a case containing steam, or a case of wood, or of other nonconducting substance, which should keep it always of an equable temperature.

"The improvement of Newcomen's engine, so far as the saving of steam and fuel was concerned, was now complete in Mr Watt's mind; and in the course of the following year, 1765, he executed a working model, the effect of which he found fully to answer his expectations. It worked readily with 10 lib. on the inch, and was even capable of raising 14 lib.; and did not require more than one-third of the steam used in the common atmospheric engine, to produce the same effect. Indeed, the principle of keeping the vessel in which the elasticity of the steam is exerted always hot, and that in which the condensation is performed always cold, is in itself perfect. For the steam never coming in contact with any substance colder than itself until it had done its office, no part is condensed until the whole effect has been obtained in the cylinder; and when it has acted there, it is so condensed in the separate vessel that no resistance remains: accordingly, the barometer proves a vacuum, nearly as perfect as by the exhaustion of the air-pump. The whole of the steam and heat is usefully employed; and the contrivance appears scarcely to admit of improvement.

Z

"The steam-engine," resumed the Nymph, forgetting the dispute which had given rise to the reading of the foregoing passage, "is the greatest invention, next to that of letters, which the powers of the human mind have yet achieved,-were one to designate remarkable cycles, by emblematic, or hieroglyphical figures, the steam-engine should be the type of the eighteenth century. It has in effect created, as it were by something like a fiat, a prodigious increase, not only to the adult population of this world, but of mechanics in the full maturity of skill. I have heard, that some time ago the productive powers of the steam-engine in this country were considered as equivalent to those of sixty millions of artizans. If, therefore, we consider the invention in a political point of view, it is hardly possible to estimate the accession of strength which it has given to the kingdom."

CHAP. XXI.

ADVENTURES.

"THE only remnant left among us of that romantic spirit which, in former times, sent so many of the bold peers of Christendom in quest of adventures," said Egeria one morning as she was turning over the leaves of Legh's Journey in Egypt, "is, unques tionably, the curiosity of those indefatigable travellers, who go abroad to gather fame by collecting materials for publication. The labours they un

dergo, the antres vast which they visit, and the "hair-breadth 'scapes, and moving accidents by flood and field," which they voluntarily encounter, afford matter for much musing. The very least of the hardships which this gentleman has suffered would have furnished a long chapter to the lengthiest romance-writer of the brightest days of chivalry. I question, indeed, if ever Orlando himself met with an adventure more appalling than Mr Legh's descent into the caverns of the crocodiles near Manfalout.It is not easy to imagine what could induce any Christian gentleman to engage in such an enterprise. Το say nothing of the danger, whether from reptiles or azote, the very idea of mingling, like a grub of the grave, among the dried entrails and rattling carcasses of such monsters, is equal in horror to any image that can be formed of the wildest spells and darkest enchantments of the most potent sorcerer that either pagan or knight in Palestine ever dreaded."

"Read it," said Benedict.

"We had been wandering for more than an hour in low subterranean passages, and felt considerably fatigued by the irksomeness of the posture in which we had been obliged to move, and the heat of our torches in those narrow and low galleries. But the Arabs spoke so confidently of succeeding in this second trial, that we were induced once more to attend them. We found the opening of the chamber which we now approached guarded by a trench of unknown depth, and wide enough to require a good leap. The first Arab jumped the ditch, and we all followed him. The passage we entered was extremely small, and so low in some places as to oblige us to crawl flat on the ground, and almost

always on our hands and knees. The intricacies of its windings resembled a labyrinth; and it terminated at length in a chamber much smaller than that we had left; but, like it, containing nothing to satisfy our curiosity. Our search hitherto had been fruitless; but the mummies might not be far distant,-another effort, and we might still be successful.

"The Arab whom I followed, and who led the way, now entered another gallery, and we all continued to move in the same manner as before, each preceded by a guide. We had not gone far before the heat became excessive; for my own part, I found my breathing extremely difficult,-my head began to ache most violently, and I had a most distressing sensation of fulness about the breast. We felt we had gone too far, and yet were almost deprived of the power of returning. At this moment the torch of the first Arab went out. I was close to him, and saw him fall on his side; he uttered a groan-his legs were strongly convulsed, and I heard a rattling noise in his throat-he was dead. The Arab behind me seeing the torch of his companion extinguished, and conceiving he had stumbled, passed me, advanced to his assistance, and stooped. I observed him appear faint, totter, and fall in a moment, he also was dead. The third Arab came forward, and made an effort to approach the bodies, but stopped short. We looked at each other in silent horror. The danger increased every instant; our torches burnt faintly—our breathing became more difficult-our knees tottered under us, and we felt our strength nearly gone.

"There was no time to be lost. The American, Barthow, cried to us to take courage, and we began to move back as fast as we could. We heard the remaining Arab shouting after us, calling us Caffres, imploring our assistance, and upbraiding us with deserting him. But we were obliged to leave him to his fate, expecting every moment