an angle, the piston would produce as great an effect, as if its force had been applied in the direction from M to R perpendicular to the crank R C!

It will be seen by this diagram, that if the angle formed by the connecting rod and crank, be a very acute angle, as for example when the crank is at n represented by the dotted line C n at fortyfive degrees from B, the angle between the crank and connecting rod will be equal to C n E, and although the equivalent length is the natural sine of fortyfive degrees and consequently equal to the line n v. Will Nauticus venture to affirm that the engine will have as great a power under this position, as if the force of the piston was thrown perpendicularly in the direction from W to n upon a lever whose length was equal to the line n v?

I believe, Mr. Editor, you will agree with me in the opinion, that there are plenty of Englishmen who thoroughly understand this subject, and that it was quite unnecessary for "Nauticus" to give himself the trouble to travel to France for the opinion of the Chevalier de Pambour, on steam-engine cranks. The demonstration I have here given is strictly mathematical and it is not in the power of "Nauticus" to prove the contrary.

I next proceed to correct the calculations in my communication in No. 763 of your Magazine, by using four tenths for the loss of power, instead of five tenths or one half. If we reckon one horse power at 200lbs. then allowing a loss of four tenths, it is reduced to 120lbs. only; and secondly, if the horse power be taken at 220lbs. then will it be reduced to 132lbs. only of real or effective power; thirdly, if we reckon one horse power engine equal 230lbs., which I believe is rather more than is generally allowed by the engineers for a horse power, then 230lbs. reduced by four tenths for the loss by the crank, &c., will give 138lbs. for the real effective power by that standard. But as authors are not all agreed exactly as to what force should be reckoned a horse power, I will make corrections according to all these three standards reduced by four tenths for loss, &c., so that it shall not be said that I have overrated the capabilities of Mr. Davenport's engines to the disparagement of the crank steam-engines.

Referring to No. 763, of your Magazine, and page 427, we find that an engine on Mr. Davenport's plan with the driving wheel or first mover fifteen feet diameter, would lift of absolute weight 15,000lbs. six feet high in one second, which considered as the stroke of a steam-engine of that extent, will when computed by the third standard be equal to 108, or 108 horse power nearly, by the 2d standard 113, or 113% horse power nearly, and if compared by the first standard 125 horse power.

And if the wheel of Davenport's engine be twenty-five feet diameter it would lift 69,444lbs. six feet high per second, this power compared as before with the third standard will give 5033 or 503 horse power nearly; if we computed this by the second standard we find 526 or a very little more than 526 horse power for the capacity of the engine; but if we calculate according to the first standard the answer is 578,8

=

578.7 being very nearly equal to 579 horse power.

Thus it will be seen that" Nauticus" has gained very little by his ill-natured assertion of upsetting the whole of my calculations; and I leave it for the candid and judicious to consider how very amiable his motives must be who seeks to establish a reputation of his own skill in science by casting a slur upon the distinterested endeavours of others, who have no doubt investigated these subjects as carefully and as closely as himself can have done. It will be further seen, that an engine on Davenport's plan, with the wheel aforesaid of 25 feet diameter, and the whole space required, would only be about 25 by 25 feet or very little more for the entire apparatus, which is not a third of of the space occupied by the engine room,* on board the "Great Western" steam ship, whose engine is rated at 450 horses power; but if the same space were occupied by an engine on Davenport's plan, the said apparatus would produce an effective force of more than two thousand horse power, following out the proportions given in the Mechanics' Magazine, No. 736. Let "Nauticus" controvert this if he can.

* I believe it has been stated, that the engine room on board the "Great Western," is 75 feet long, and 41 or 42 feet broad, including the stowage of about 800 tons of coals for the engine. I believe one of Davenport's of the same power would not weigh above 200 tons.

It ought to be observed that the great object of these calculations and investigations is to enable us to determine beforehand, what should be the size of an engine capable of performing any quantity of work required, and that although the steam-engines, as does hereby plainly appear, are four tenths less powerful than what they are commonly thought to be, yet this is no disparagement to the manufacturers of them, as they furnish engines that will do what is stipulated for; and for the clearer understanding of this subject, it would be well to distinguish between the computed nominal power, and the real and effective power of steam-engines. Thus for example, the engine on board the "Great Western" steam ship, is rated at 450 horse-power; but if this be reduced by allowing four tenths by the cranks and connecting rods, &c., will give 270 for the number of effective horse-power; and since in these cases, whether we calculate by the real or nominal power, we see this is sufficient to carry a ship of 1400 tons burden with rapidity through the ocean, and will therefore serve us as astandard to regulate the size of the engine and other machinery, for any other ship, whether larger or smaller than the "Great Western" steamer. And it will further be seen by referring to my corrections contained in this letter, that an electro-magnetic engine with the driving wheel 25 feet diameter would be 53 horsepower, 76 horse-power, and 129 horses power greater than the power of the engine of the " Great Western," according as we calculated by the third, second, or first standards for a horse-power beforementioned.

I will further call your attention to the important fact, that "Nauticus" has unwittingly, and no doubt quite unintentionally furnished ine with one of the most powerful arguments in favour of Davenport's engines; and with the weapons he has provided me I shall proceed to combat him, and to prove their (Davenport's) vast superiority over steam-engines. In the beginning of "Nauticus's" letter he snarls at my shewing,

"that Davenport's would be equal to a steam-engine whose piston has a stroke of 6 feet in length and making sixty strokes per minute; and consequently the space passed over by the piston will be 6 feet x 60 = 360 feet per

minute!" ("Nauticus" then proceeds to state,) that" the utmost limit prescribed by Watt and others is 220 feet per minute, and that this is never exceeded except in locomotives, where the rapid motion of the piston is found to be so distressing to the working parts, that those concerned therein are seriously contemplating to reduce the speed to the above standard of 220 feet per minute, and that hence the deductions referred to are totally incorrect."

I

Whoever will take the pains carefully to examine this quotation from "Nauticus," will soon see, that he either did not understand, or else that he has misrepresented the meaning of my communication: he has treated the whole matter as if Davenport's was a piston engine, which performed sixty strokes per minute of six feet in length each stroke. never stated any such thing; what I stated was by way of comparison, that an electro-magnetic wheel on Davenport's plan 15 feet diameter would lift 15000lbs. 6 feet high per second; and that if the wheel was 25 feet diameter it would lift 69,444lbs. 6 feet high per second, which would of course be equal to the pistons of steam-engines, each respectively lift ing the same weights and moving through the space of 6 feet per second. I did not assert that any steam-engine actually did this; but I shewed that Davenport's engines of the sizes I had there stated would equal steam-engines of certain dimensions that might do this; what I there stated was to enable the reader easily to understand and compare the capabilities of the electro magnetic with the powers of the common steam-engines.

To acknowledge that the velocity of the pistons must not exceed 220 feet per minute, is indeed very unfortunate for the admirers of piston and crank movements. "Nauticus" did not perceive that by this avowal he had declared that there exists a striking imperfection in steamengines, which arises from the violent concussions of the piston upon the connecting rods and crank, which when the motion of the piston is very rapid acts like the sudden blow of a hammer, and it is this which occasions the wear and straining of the working parts. But there are no such objections against the electro-magnetic engine, the very power of which originates in a circular movement of the driving wheel itself, and has

no jerking nor straining of the working, but is smooth and uniform in its motion; and moreover as a first mover is not limited in its velocity to 220 nor to 2200 feet per minute; for it appears that Mr. Davenport's wheel makes from 600 to 1000 revolutions in a minute! There is no danger of explosions, and of destruction to the vessel and passengers, as in steam-engines. These peculiar mechanical properties together with the great saving of room and expense, cannot fail in establishing the use of Davenport's invention, and ultimately throwing the common steam-engine completely into the shade.

The person who does not know that engines may be made to act by other means than by steam produced from boiling water, surely cannot boast of being profoundly versed in mechanical science; there are certainly many things that "Nauticus" yet never dreamt of in his philosophy.

I had intended to have now written something concerning a remedy or substitute for the crank in steam-engines, but must defer this, till some other opportunity, and in the mean time subscribe myself, as I have been for fifteen years past,

Sir, your's very respectfully, THOMAS OXLEY. 2, Elizabeth-place, Westminster-road, April 26, 1838.

NOTES AND NOTICES.

Great Mongolfier Balloon.-An experimental trial of an immense machine was made on Tuesday, on the borders of Epping Forest, in the presence of the constructor and several scientific gentlemen connected with the undertaking, for the purpose of trying the effect of a newly-invented furnace by which the balloon is to be filled with heated air, instead of the imperfect open brazier used by Mongolfier, Pilâtre, Rozier, and others, in their ascents from Paris some years since. By means of this invention the possibility of any spark coming in contact with the machine during the inflation is entirely avoided, and although at one period of the experiment the temperature was raised to two hundred degrees, not the slightest appearance of danger was visible. So powerful were the means used to obtain the requisite degree of rarefaction,

that the vast machine was completely filled in eight minutes, and had then an ascending power of 1,200 lbs. exclusive of the furnace and car, the latter of which alone weighs, when adorned, 300 lbs., and is 15 feet long by 8 feet wide. Three persons ascended to a considerable height, but were restrained from making an aerial excursion, it being intended only to ascertain correctly the capabilities of the balloon. All the persons present expressed themselves extremely gratified with the perfect success of the experiment. The first ascent will take place from the Surrey Zoological Gardens, when the builder and two other gentlemen well versed in aërostation will ascend.-Essex Paper.

The Atlantic Steamers.-Much anxiety is evinced to learn the particulars of the voyage out of the Atlantic steamers, Sirius and Great Western, and especial interest is attached to the former, from the circumstance of her being furnished with Hall's condensers, which will thus undergo a decisive trial. The last news of her was on the 14th April, when she had been ten days out, and she was then gallantly steaming on at the rate (it is said) of two hundred and fifty miles a day. Both she and her opponent, it will be recollected, must have met on the outset of their passage with the strong westerly gales which prevailed in the beginning of April, and been much retarded in consequence. It is therefore tolerably certain that neither would arrive at New York within the "expected" time,-twelve days, although it may be anticipated that they will have beaten the sailing packets by a "pretty considerable way."

carry the

French Steamer in the Thames.-Hitherto all the steam-vessels frequenting the port of London have been virtually, if not ostensibly, of British ownership and origin. The French, however, have at length resolved to enter the field, and war into the enemy's quarters." A splendid new steamer, the "Phoenix," has been built at Havre for this purpose, and has just commenced running between her native port and London Bridge, between which places she intends to take up a regular station. She belongs to a French company, who are determined, if possible, to reap some of the benefits of the immense intercourse between the two capitals of England and France, by water as well as by land.

Sir John Soane's Benefactions.-The Soane Museum has just re-opened for the season, under the same regulations as last year,-regulations which operate to prevent any thing like the free admission of "the public." The "Soane Medal" is to be adjudged by the Institute of British Architects, and the subject for the present year is "the restoration of one of the ancient Baronial Castles of Great Britain." The first annual distribution of Sir John Soane's donations by will to distressed architects and architects' widows is also on the eve of taking place.

Charcoal Fuel.-In the London Magazine for December, 1758, there is the following paragraph in a division of the work called the "Monthly Chronologer," under the date Tuesday, Nov. 26:"Some persons having been almost suffocated lately by sleeping in a room wherein was a charcoal fire, it has been declared that experiment has proved, that charcoal fire wetted with salt dissolved in water will have no suffocating quality."

Complete Sets of the Mechanics' Magazine may now be had, twenty-seven volumes, half-cloth, price 11 78.

CHANTER AND CO.'S PATENT SMOKE

BURNER.

This invention essentially consists in so arranging the form of the furnace and position of the bars, that the fuel is regularly advanced by gravitation, without the aid of machinery, or any apparatus besides the simple instruments in common use for the management of furnaces. This is effected by placing the fire-bars at an angle of about 45°, and sloping the bottom of the boiler in the same degree; the carbon and various more inflammable gases are set free at the commencement of combustion at the upper end of the furnace, and being charged with the oxygen of the atmosphere proceed through and over the fire, which increases in heat to its lower end, gradually subjecting the less combustible gases to perfect combustion. Saving in fuel is thus effected; for in the present furnaces, these latter gases are not only passed off unconsumed, but by preventing the ignition of more combustible materials necessarily waste a large portion of the fuel. Thus the effect, in the operation of this furnance, may be stated to be that of obtaining, at the termination of the furnace, that intense degree of heat indispensable to the entire combustion of the various substances emitted from the burning fuel. The invention is exhibited in Mr. Chanter's specification in twelve different forms, shewing its application to various descriptions of furnaces. The engraving on our front page shews the application of the inclined fire-bars to a locomotive-engine furnace. The secondary furnaces beneath the principal fire-bars are for the purpose of heating the air as it enters the ash-pit; a hot blast is thereby obtained to effect the more complete combustion of the fuel. It appears from numerous testimonials, given by the first engineering authorities, that the intended object is effectually performed-the most common coal being burned without any appearance of smoke from the chimney.

STEAM NAVIGATION TO INDIA.

Sir, The pamphlet recently published by Sir John Ross for the purpose of showing the practicability of forming a steam communication with India via the Cape of Good Hope, has just come under my notice. I fully concur with him in opi

nion as to its practicability, but cannot yet bring myself to the belief that it can be accomplished in the short period he has stated (less than 50 days), for the following reasons:-First, assuming the distance to be about 12,000 miles by the most direct route; if the steam-vessels were able to maintain an average rate of 10 miles per hour, fifty days would be required for the voyage, exclusive of the necessary delays for receiving additional fuel on board, cleaning the machinery, &c. I have not at present met with any steam-vessel in the course of my somewhat extensive observation, that has been able to maintain such an average speed for several consecutive days, and my opportunities for acquiring information relative to the actual performance of steam-boats, are very frequent. Some few boats will maintain ten miles an hour for 30 or 40 hours, or even 80 hours; yet these fast vessels would not be found to maintain an average of quite ten miles an hour during the whole of the voyages made from the 1st of January to the 30th June, or from the 1st July to the 31st December, in the British seas, with a fair average cargo on board; although these voyages are comparatively so short that the machinery may be reasonably expected to run the whole passage without requiring to be stopped for a sufficient length of time to cccasion any material reduction in their average rate. Some months since I had an opportunity of examining the account (regularly kept) of the performance of some of the fastest boats plying between Glasgow and Liverpool, which fully bears me out in the preceding statement. The reports of the speed of steam-vessels are very generally exaggerated. An instance recently came to my knowledge in which it was confidently stated that a speed of 14 miles an hour had been attained by a new steamvessel. One of the gentlemen present at the trial proved that the speed attained was only from 11 to 11 miles per hour, and this with the engines in the best possible condition. His statement was confirmed by the facts, that the number of strokes and size of the wheels would not admit of her going at a greater speed unless the resistance of the boat is reduced in the same ratio as her velocity through the water is increased. Something like this theory was advanced by a gentleman upon whose work some remarks were