process of cooling is finally completed, by making the air pass through between a number of tubes in which there is a current of cold water, and thus far the heat caunot be made available again; but the portion which is abstracted in this way is very small.

As a sufficient expansive power could not be attained in so small a space without greater alterations of temperature from using air of the common density of the atmosphere, the air used is pretty highly compressed, and a much greater power is thereby obtained upon a given area of the piston.

A small air-pump, worked by the engine, is therefore necessary to keep up the air to the requisite density; but very little power is expended on this all that is required of the pump, after the engine has been once charged, being to supply any loss of air that may arise from leakage, which is found to be very trifling.

The machine has been working occasionally for above six months, and it has been proved to be capable of performing advantageously the amount of work which the inventors had anticipated from their calculations and previous experiments. It has now for upwards of a month been driving all the machinery at the extensive engineering works of the Dundee foundry, which a steam-engine of approved construction had hitherto been employed to do; and it has been ascertained that the expenditure of fuel is, cæteris paribus, less than one-fifth part of what was required for the steam engine; but as considerable improvements are contemplated in some of the details, it is confidently expected that a much greater saving will eventually be effected.

The whole machine, including its furnaces and heating apparatus, stands in about the same space that a steam-engine of equal power would occupy without its furnaces and boiler. Taking into account the saving of space along with the vast economy of fuel, this invention must necessarily be of immense importance for all ordinary purposes requiring motive power. As an instance, it would reduce the expense of the power employed in driving machinery in Dundee alone by at least £25,000 or £30,000 a year. But, viewed in reference to the purposes of navigation, it must lead to results still more extraordinary, and will render a voyage to India round the Cape by machinery a matter of perfectly easy accomplishment.

IMPROVEMENT IN STEAM NAVIGATION.

We have heretofore given a description of the mode of applying steam power to navigation, by means of the Archimedean screw and Ericsson's propeller. The London Morning Post gives the following account of an experiment which was recently made in the Thames, of an approved mode of applying these improvements, in connexion

with the rotary engine. One great objection to their adaptation hitherto, the difficulty, (except by complicated gearing,) of getting up the necessary number of revolutions, appears to be entirely obviated by Mr. Beale, as from the description below, the propeller may be driven direct from the engine shaft, at a very great speed.

"The steam principle seems, moreover, to be very materially accelerated by the great improvements in the working of it. The rotatory engine, for instance, is calculated to bring about great results in connexion with the steam process. It is a wonderful simplification of the machinery now in use, and much less expensive. The difference in this respect is to be found, in perhaps equal degrees, with reference both to the works themselves and the consumption of fuel. It is not often that we, of the city department of the paper, find an opportunity of indulging in water excursions; but an opportunity being afforded us of witnessing the performances of the newly-constructed vessel called the Anti-John Scott Russell,' we passed an hour on board of her on the river, and certainly we have seldom experienced a higher gratification. This little model is 53 feet in length, by 6 feet in width. The paddle-wheels are 6 feet 5 inches in diameter, and they make from 60 to 70 revolutions per minute, propelling the boat at the unequalled, and we may say, for a small boat, unheard-of velocity, of at least 12 miles per hour. The engine is one of eight-horse power, 14 inches in diameter, and 9 1-2 inches in length. It is worked on the condensing principle, and makes 270 revolutions against 60 of the paddle wheel. The boat, we are informed, has been repeatedly tested during the last two months, and it appears that no difficulty whatever has occurred with the engine, which is in excellent working order. Mr. Beale tells us, that he has in a state of forwardness an engine constructed upon the same simple and beautiful principle, of sixty-horse power, intended for actual business. The model boat has been named after Mr. John Scott Russell, with the prefix of anti,' because that intelligent gentleman has very boldly and publicly asserted, that to make as effective a rotatory as an ordinary reciprocating steam-engine is impracticable.'

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"The little craft shot like lightning through the water, and it were superfluous to add, that she attracted, in a singular degree, the attention of the seafaring persons she encountered on the river. The figure-head represents Mr. Beale taking what is called 'a sight,' and, if the skeptical Mr. Russell has not yet seen it, we hope he will lose no time in doing so. Where success is thus complete, the gilded jeu d'esprit is very pardonable, and, with all his misgivings about the rotatory principle, we venture to say that he will so consider it."

STEAMBOAT LITTLE WESTERN, ON THE THAMES.

A LONDON journal gives the following description of the new steamer Little Western, and of an experimental trip on the Thames, which was attended by a number of officers of the navy, and other scientific gentlemen. She left her moorings off the Brunswick Hotel, at a quarter to 11; the tide then running down, and the wind blowing from the south-west. There was, however, but little wind, and the weather was clear and pleasant. She was accompanied down the river by one of the fastest boats, viz., the Railway, for which she waited off Galleons, and with which she contested head and head to Gravesend. The speed of the Little Western is extraordinary; she reached the Nore Light within 2 hours and 55 minutes from the time of starting, and returned to Blackwall within 2 hours and 25 minutes. The distance is 44 miles. This vessel is built on an improved principle. Her tonnage measurement is a fraction beyond 721 tons. She measures between perpendiculars 200 feet, measurement over all 216 feet. Her keel measurement is 195 feet. Her breadth, clear of her paddle-boxes, is rather above 27 feet; and her breadth over all exceeds 47 feet. Her deck is flush from stem to stern, and she has two masts. Her internal accommodations are very good, as may be surmised from the measurement of her saloon and cabins, &c. The length of her saloon is nearly 44 feet, and the room is elegantly and commodiously fitted up, without being gaudy or fantastic; it is also a good height, and is 24 feet wide. The ladies' cabin is nearly 20 feet long. The engines, which are horizontal and low pressure, are of 80-horse power each. Altogether she is a most elegant craft, and an admirable sea-boat. She has weathered a gale off the Land's-end, and proved her capability to contend against a rough sea and a heavy wind. This vessel was built at Bristol, by Messrs. Acramans, Morgan & Co. She is a vessel excellently adapted to the London and Ramsgate station. Her prodigious speed, superior accommodation, and tractability, render her peculiarly desirable for trips, in which convenience and rapidity are imperative.

THE ARTESIAN WELL AT GRENELLE.

WE have before called attention to this magnificent work of modern science, [Mon. Chron. Vol. II. p. 93.] It is with regret that we have seen recent announcements, that some difficulty has taken place in the work, in consequence of the leakage of the joints of the pipes. The following extract from a report of the French Academy will show the state in which the works at present are:

"A part of the accidents and difficulties at the Artesian well at Gre

nelle, which have taken place in the course of the four or five months since these subterranean waters have been spouting up, have been made known to the public. But there is no end to these tribulations, and the definitive success of this great work is not altogether matter of certainty. M. Arago, at the late session of the Academy, gave a somewhat melancholy picture of the present state of that fountain, which has inspired such great hopes. The first system of interior pipes did not succeed, and the water filtered through the spaces, which were left between ends of the different pipes; and it was found necessary to draw up all these pipes, and endeavor to introduce one made in a single unbroken piece. The undertaking was great and bold; but it happened that from the impossibility of screwing this copper pipe to a part of the first tube, which remained fixed at the bottom of the well, the water again flowed on the outside as well as within the new pipe. The result was, therefore, the double flow of the water, without and within. The first, however, prevailing over the second, in consequence of the obstruction made by the gravel to the free passage of the water, the pipe became flattened in several parts, and twisted into the form of a corkscrew, so that now, neither the water nor the sounding-rod can pass into the centre of the tube, and it has as yet been found impossible, with the greatest effort, to draw up the tube from the ground, where it remains firmly fixed. From the great confidence, however, which is felt in the skill of the artist who superintends this work, assisted by the advice of the learned men by whom he is surrounded, no doubt seems to be entertained, that these new and powerful obstacles will be overcome, and that the city of Paris will reap the fruit of the sacrifices which she has made in this laborious undertaking."

It will be remembered that the well at Grenelle is undertaken by the city of Paris for the supply of water to one of the abattoirs or slaughter-markets of that metropolis.

CUTTING STONE BY MACHINERY. PATENT IRON MASON.

A MACHINE under this name, (for which a patent has just been taken out,) is about to be erected in one of Mr. Nelson's quarries at Woodside, Glasgow. The stones go into the machine rough as they come from the quarryman's pick, and come out polished ashlar on the surface, and cut parallel and square on the sides, fully prepared for the builder, and this at an expense of not more than a fourth of work done by hand. The present machine is calculated to do the work of 250 men, reckoning only six hours' work out of every ten. The machine has been constructed by Messrs. P. W. M'Onie & Co., engineers, Scotlandstreet, Tradeston, the design and arrangements being the work of Mr. P. M'Onie, of that firm. We understand the machine, with the ex

perimenting and patents, has cost £1,000, although new machines of the same size can now be made for one third of that sum, and smaller ones proportionably cheaper. - Practical Mechanic.

PHOTOGRAPHIC PORTRAITS.

A VERY desirable improvement, and one materially differing in its nature from all former steps in photographic art, has recently been introduced by an invention of Mr. Fox Talbot, for which a patent has been taken out. The improvement consists in the portraits being taken on paper, instead of on metallic plates, of their being indelible, of the extreme accuracy of likeness, the breadth of light and shadow, the general pictorial effect, and the capability of the portrait being multiplied into many copies or transcripts, or facsimile representations, without the sitter being required to sit for each portrait. They resemble sepia drawings, and are exceedingly true. The sitting requires but a minute, or two minutes, according to the brightness of the day. The paper is prepared with salts of silver, and subjected, by an apparatus furnished with glasses, to the rays of light, and the likeness is, as it were, absorbed by the paper. A description of this process cannot be conveyed very clearly in a written description; nor is it necessary that it should be, because it is easy for all who feel an interest in art to avail themselves of a personal inspection of the process by making a proper application to the artist. The process is called the "calotypic" process. It affords very curious evidence of the agency of light in effecting chemical changes, and it shows how science may be made subservient or auxiliary to the advancement of the fine arts. The portraits obtained by this invention may be placed in portfolios or suspended in frames as ornaments and reminiscences of friends and relatives; and the faithfulness of resemblance may be relied on. There is no distortion of feature, and none of that hardness, by which common photographic portraits are disfigured, and being on paper, defects may be amended by the pencil of the artist, and judicious additions introduced, by which a picture as well as a mere portrait may be secured. -London Times.

THE DEAD SEA.

AT a recent sitting of the Academy of Science, at Paris, M. Arago read a communication from M. Rusiger, a German geologist, on certain geometrical observations made in order to ascertain the relative altitudes of the Dead Sea in Palestinc, and the Mediterranean. It