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for the painted ceiling at Whitehall. Now, all that is required for this useful imitation is black and red; for with these two colours, and the ground, which is yellow, may be produced a thousand different tints." Particular instructions for imitating the marbles most in request, with a beautiful specimen of each, are then given. These are followed by some highly useful observations on preparing grounds, and polishing, which, did our space permit, we would willingly have transferred to our pages.

The whole plan and execution of the work is highly creditable to the artistical skill of Mr. Moxon, who, in thus laying before his brethren of the trade, (or, as the grainers say, the profession,) correct models for their study and imitation, has done much to promote a taste for simplicity and chastity of design, which, being founded in truth, never fails to realize more or less of the perfection of beauty.

ON REMOVING THE HEATING EFFECT FROM THE SOLAR AND OXY-HYDROGEN MICROSCOPES.

Sir, I have read lately, in the Philosophical Magazine, vol. x. p. 184, a description of a method of cooling, by a current of air, the heating effect on the objects exhibited in the solar and oxy-hydrogen microscopes. The object is stated to have been accomplished by the use of a pair of domestic hand-bellows, and with complete success, the thermometer indicating the temperature to be as low as 60° Fahr.; so that, to quote the words of the writer, "our solar and oxy-hydrogen microscopes, instead of being used for purposes of amusement only, and limited to the exhibition of objects which are unaffected by heat, may henceforward be employed for purposes of scientific investigation, and thereby assume the more important rank of valuable philosophical instruments." In furtherance of these views, I beg to propose the use of a revolving disc of glass, the lower half of which ought, probably, to be immersed in a trough of water, the upper portion passing over the objects in a space between them and the condensing lenses. Not having an instrument of the class by me, I have not had an opportunity of testing the value of this suggestion; yet there are, no doubt, some of your readers

in possession of one, and if they will do so for me, I shall be very happy to hear the result. The glass disc may be made like the plate of an electrical machine, and may be conveniently set in motion by a lowering weight.

I am, Sir, yours, &c.,

S. M. NEWSAM.

CONDENSATION OF STEAM BY COLD AIB. CRADDOCK'S PROCESS.

Sir,-With your permission I will lay before your readers an account of my patent condenser for steam-engines, and of a series of experiments made therewith; the latter of which will, I trust, demonstrate that the condensation of steam by the cooling effect of air, hitherto considered impracticable, is not only within the reach of possibility, but can be effected with such facility as to render its adoption general in those situations where a supply of water is not to be procured.

The peculiar feature of my invention is, the communication of a rapid motion to the condenser; independent, of course, of the motion which the vessel or locomotive may have, to which my condenser is attached. It will be unnecessary for me to detail my preliminary experiments, or the various forms which I have given to the condenser during my investigations: I will therefore at once describe the apparatus in that form which, from my present experience, seems to me the best. A hollow axis is supported by proper bearings in a vertical position. The lower end, or that at which the steam is introduced, is open, and works on a pivot fixed on the bottom of a chamber, on the top of which is a stuffing-box, through which the axis passes. Near the upper or closed end of the axis is an enlargement or chamber, from which proceed, at right angles to the axis, a number of radial hollow arms, into each of which the ends of a series of small copper tubes are inserted; these, of course, are parallel to the axis; their lower ends are inserted into other radial arms fixed near the bottom of the axis, and similar to those at top, excepting that their ends do not open into it. The radial arms at the bottom are all connected by their ends opening into an annular chamber. A

NEW AND SIMPLE METHOD OF OBTAINING MEZZOTINT GROUNDS.

rapid rotary motion is given to the condenser by the steam-engine to which it is attached, the result of which is the cooling of the apparatus, and, consequently, the condensation of the steam which has been introduced into the small copper tubes. The condensed steam or water falls into the lower radial arms, and is thrown from thence into the annular chamber by centrifugal force; a small pump is affixed to this chamber, and its piston-rod is attached to the clip of a fixed eccentric supported round the movable axis of the condenser. As the pump travels about this eccentric, its piston-rod works to and fro, and the water is removed from the condenser. The arrangement of the minor parts of the apparatus, such as the conveyance of the water to the boiler, the connexion of the air-pump, &c., cannot be illustrated without drawings. I may just remark, here, that the force-pump for the removal of the water is not absolutely necessary, as the air-pump may be made to effect that object. My experience, however, demonstrates that it is effected to greater advantage by its use.

I have attached a condenser of this kind to a high-pressure engine of five horses' power, and, by giving it a velocity of 11 miles per hour, the water is drawn off at a temperature varying, with that of the air, from 90° to 120° Fahr. The column of mercury supported by the vacuum is not quite so high as it should be, according to the temperature of the water; this, however, is owing to the imperfection of some of the joints in the condenser, and will soon be remedied. The power gained is more than double that required to work the condenser and air-pump. The amount of surface required to condense a given number of cubic feet of water per hour depends on the velocity at which it is intended to work the condenser, and the temperature at which the water is drawn off. It does not appear to me advisable to draw the water off at a temperature lower than 150°, for a given abstraction of heat at a lower temperature affects the height of the mercurial column much less than at a higher; and any one familiar with the law according to which heat passes from one body to another need not be told, that the same surface will condense much more steam into water at 150° than at 100°. A condenser having a velocity

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equal to 20 miles per hour, and the water being drawn off at 150°, will require about 20 square feet of surface per cubic foot of water per hour. The strength of the copper I have hitherto used is 1 lb. to the square foot, but I intend using it much lighter in future. The weight of a condenser equal to condense 10 cubic feet of water per hour will be from 8 to 10 cwt.

Besides the advantages which my mode of condensation possesses, in those situations where a supply of water cannot be had, I believe it possesses other, and scarcely less important ones. By my condenser returning the water to the boiler, I am enabled to use a tubular boiler, without experiencing that inconvenience which almost precludes their use in combination with the ordinary system of condensation, namely, the liability to become choked up by the deposit from the water. Although the condenser with which I am working is far from being tight in its various joinings, I have worked my engines constantly, for four days, without adding any water to the boiler; and I have no doubt that the condenser and engine I am now fitting up, and to which I hope very soon to be able to call the attention of engineers, will give results even more satisfactory than those at present obtained.

In conclusion, I have only to remark, that the apparatus and engine with which the above results were obtained may be inspected by any parties who feel interested in the matter, at my manufactory, 350, Coventry-road, Birmingham. I am, Sir, &c.,

THOMAS CRADDOCK.

NEW AND SIMPLE METHOD OF OBTAINING MEZZOTINT GROUNDS.

Sir,-It gives me some pleasure to be able to announce that I can form a tolerably good mezzotint "ground" on a plate, by passing it along with a piece of common sand paper five or six times through the rolling printing press, with rather a tight pressure. The depth of colour, when printed from, does not quite possess the intensity of those executed in the usual manner; but the method answers exceedingly well for prints which are intended to finish in colours. Sir, I remain your obedient servant, LAURENCE BRUNTON.

March 14, 1842.

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the back bar g, which turns in brass bearings, fixed to the legs of the lathe as shown, and to the end of which is fixed the upright rod d, communicating with the crank e, by the connecting rod f.

It will be seen, on reference to fig. 1, that the crank e (which is fixed to the shaft g, at the driving wheel,) has a groove in the middle of it, which allows the pin, to which the connecting rod f comes, to be shifted to or from the centre and made fast at any required distance, as the case may require, by a nut and screw at the back.

H. C.

APPLICATION OF THE ELECTROTYPE TO THE MULTIPLICATION OF GRADUATED INSTRUMENTS.

Sir,-In your last Number, which has just been received, I observe mention made of a new application of the electrotype, by M. Peyré, for multiplication of graduated instruments. As the first to

make the subject public, doubtless he has a right to the invention. The method was, however, proposed by me in December, 1840, for producing graduated astronomical instruments from an original

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66 DOUBLE ACTING ROTARY ENGINE COMPANY."

one; also scales, dials, &c.; and probably
for producing plates of marking in in-
sects' wings, &c., for printing from."
The plan was tried by me, but only to a
limited extent, for the production of
scales; the result of one experiment
being an electrotype scale, divided into
100 of inches. A variety of circumstances
prevented me from paying immediate at-
tention to the matter, or I should have
communicated the results to you. The
plan of M. Peyré will, I have little doubt,
be of value, and the public will be in-
debted to him for making them acquainted
with the further success of his process.
It has occurred to me, also, that the
electrotype process might be successfully
used for producing tools for re-grinding
or polishing specula, as the tool might
thus be made from the speculum itself,
if of good figure; and any number could
be made from the original tool, as those
in use altered in figure. Tools might
also be made from lenses, for the same
purpose. If you think these hints likely
to be of service, perhaps you will insert
them in the Mech. Mag., and oblige,
Sir, yours respectfully,

Sidmouth, March 18, 1842.

N. S. HEINEKEN.

"DOUBLE ACTING ROTARY ENGINE COMPANY."

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We learn from some papers which have been forwarded to us that a project is on foot for the formation of a company under the above title, for bringing into use a "new motive power," which is considered to be incomparably superior to steam, and therefore infallibly destined to supersede it every where and for every purpose. Mighty agent" as steam is, this is represented to be mightier still. To the application of steam there are certain practical limits, but this new power is a power which 66 can be carried to any extent." The cost, too, is not simply less than that of steam-it is "infinitely less." People may send their present steam engines to the marinestore shops, and obtain as much for them at old metal prices, as will suffice to build them "infinitely" better engines on this new power plan. "The sale of the rejected metallic parts" is to defray "nearly" all expenses of every kind, both present and future. For, once erected, an engine on this new plan is to cost nothing, or next to nothing; "no fuel, of

66

249

any kind is required"-no "daily maintenance"-it is to work without any wear and tear," saving only the "mere loss occasioned by friction"-all that is wanted absolutely is, but a little oil or tallow to lubricate the parts occasionally -once a twelvemonth or so! Some of our readers (we hope not many, however) may by this time have pictured to themselves that "galvanism, or electricity" must needs have something to do with this new miracle of invention. No such thing-the mystery lies a good deal deeper. Neither galvanism nor electricity is of virtue enough for the accomplishment of such wonders; and "for this simple reason," says Messieurs the projectors of the "Double Acting Rotary Company," "that they are convulsions of nature never intended by a Divine Providence for the use of man"!!

Where then lies the grand secret? In a narrower compass than any thing so extraordinary was ever perhaps shrouded before-in a nut shell verily. You have but to place an empty cylinder, one half in water, or any other fluid, and one half in a vacuo—that is, literally, all you are required to do-and you shall cause it to revolve continually, and with any degree of power you please-remembering only to make your cylinder large enough! And for this other "simple reason:" there are 66 two tendencies to move" in the cylinder the tendency of the part in water to rise, and the tendency of the part in vacuo to fall, and "the two tendencies being auxiliary to each other, necessarily produce a continually revolving motion !!!"

The thing is so like a joke, that it may be difficult to persuade our readers we are not joking. We describe the invention, however, with strict fidelity, as we find it described in the printed papers of the projected Company now before us. The inventor and his friends then must have deceived themselves? One would in charity think so; but if they have, it is not at least without sufficient pretence of ability to judge rightly, and without a great display of pains to go on sure grounds. The inventor is a "Count de Predaval," "who styles himself Engineer in the Service of his Imperial Majesty the Emperor of Austria;" and the Count, as a good and respectable engineer worthy of such distinguished patronage would do, has been careful not to submit his inven

tion to the public till "after the strictest experimental investigation has perfectly proved its merits." Nay more, with a view to obtain the corroborative evidence of scientific men on his invention, it was submitted to several eminent engineers;" and a report of "one of them" is given at length, which we are told "vouches for the excellence and applicability of the principle of the invention," as in sooth it does. Who the other "eminent engineers" were, and what they said of it we are not told. The Count, probably, thought that after "one of them," and he, no doubt, the most eminent of the lot, had said his say to such capital purpose, there was no need of further testimony. Would any one, after quoting a Wellington on a point of military skill, think of calling to witness either a Colonel Toby or Corporal Trim? But who is this selected "one"-the most eminent among the eminent-the Count de Predaval's Wellington of engineers ? The Report is signed "Edward Lomax," and dated from "2, Queen-square, St. James'spark." We must candidly own that we never heard of the name of "Edward Lomax" before, far less of the engineering eminence attached to it. We live out of the world, however-the Count de Predaval in it, (not without some dark intent, we fear, to make of it "his oyster;") and the Count de Predaval says

"Mr. Edward Lomax, of 2, Queen-square, St. James's-park," is an "engineer," and an "eminent" one, too; and the Count de Predaval is himself an "engineer," and "in the service of His Imperial Majesty the Emperor of Austria," &c. &c. &c.

Do not all these things, then, satisfy us? We must in sober seriousness say, they do not. We have no respect for 66 experimental investigations" which prove impossibilities-things which could never have been proved; and must doubt the mechanical knowledge and ability-if we may not the titles and the "eminence "of those who "vouch" for them. We protest that we never, in all our experience, met with any thing more ridiculous than the pretensions contained in this "Prospectus" of the Count de Predaval; nor any thing more elaborately absurd than the "corroborative" Report of his friend, the Wellington of engineers, "Edward Lomax." The scheme is a veritable perpetual motion, and one of

the most-if not literally the most-nonsensical and visionary of its class.

It may be asked, why, if it be so foolish a thing, we put ourselves to the trouble of this public exposure of it? We will tell our readers why. Had the scheme been left to depend on its own merits, or even on the authority of Mr. Edward Lomax -" eminent" as that individual may be -for acceptance with the public, we should not have thought of saying a word about it, feeling, as we should have done, well assured, that it could dupe nobody. But at the head of the "Prospectus there are the names of a number of persons paraded, as constituting a "Provisional Committee" for the management of this projected "Double-acting Rotary Engine Company;" and among these there is one name which, if it were placed there with the consent of the owner, would of itself command for the plan the confidence and contributions of thousands. It is the name of one of our most learned Professors of a gentleman of real and deserved eminer.ce for his scientific acquirements, and scarcely more distinguished for academic lore than for practical wisdom, strength of judgment, and keenness of discrimination. Who, knowing any thing of Professor de Morgan, would think of asking whether it was a piece of moonshine or humbug to which he had given the sanction of his name? Or who, with money to spare, would hesitate much about paying down a few pounds to be one of "the first hundred" to share with the worthy Professor in the golden harvest of which M. the Count de Predaval offers to make them partakers, and in the "liberal premium" which the said "first hundred " are to have into the bargain, for benefiting themselves? Here it is the danger lies: here our reason for bidding all and sundry-beware! We have the authority of Professor de Morgan himself for stating that he never heard of this "Double-acting Rotary Engine Company," till he saw his name at the head of the Prospectus; that be knows nothing whatever of the scheme, or of its inventor, or of any of his associates; and that he utterly repudiates all connexion with them and it. We think our readers will agree with us, that this looks like something more than being selfdeceived. People do not commonly use the names of other people, without their knowledge or authority, for any other purpose than that of wilfully deceiving others.

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