the dust into mud, is very injurious to the road, and merely changes one nuisance into another-dust into mud. A great source of waste, both to those who use and to those who repair a road, is to allow it to be dirty. The draught on a dirty road is twice as heavy as on a clean onethat is, a horse must exert double force to draw his load with the same speed. The cost, however, of employing double force is so great, that the expedient of diminishing the speed is generally adopted, as a horse can exert greater pulling force at a slower pace,-less power being required to carry his own body. It often happens that the extra resistance occasioned by dirt diminishes the speed one-fifth or one-fourth. The effect of the dirt, therefore, is to increase the work by twenty or twenty-five per cent. It will easily be believed that such a waste far exceeds the cost of the most perfect cleansing. This is the case when cleansing is done by scrapers (the greatest enemy a macadamized road has to contend against). By their use the stones are dragged from their places, and the adhesive dirt is not effectually taken away. Sweeping is the only mode of cleansing that should be allowed, either on streets or on turnpikeroads.

Sweeping by the wide brooms of Mr. Whitworth's machine is preferable to all other modes of cleansing yet tried. It must be evident, that the fact of these wide brooms sweeping longitudinally, with a pressure that can be adjusted according to circumstances, tends powerfully to preserve the road and to consolidate its surface. They press most upon the ridges, and least upon the hollows, thus tending to reduce the former, and fill up the latter. When the dirt is stiff, and adheres firmly to the stones, it should first be well watered, when it may be completely removed by the machine, without disturbing the crust, leaving the surface firm and compact. The use of water for this purpose has been objected to by high authorities, on the ground that it does remove the useful grit; but the contrary has been proved by ample experience. I have found that the use of the sweeping-machines, with the proper employment of water, has reduced the amount of material required for the repair of roads in Birmingham one-third -namely, from about 20,000 to 13,000 cubic yards. The first-named amount is the average for seven years preceding the introduction of the machines,-the latter of the three years subsequent. I communicated these details to a friend in London, and he determined to test their correctness. The following is the result of his experiment to settle whether useful grit was or was not removed by water and machine sweeping.

On the 22nd of March last, the Quadrant, Regent-street, was covered with a thick layer of dirt, which was causing great annoyance as well as injury to the road, but could not be removed by scraping without removing also much of the new stone to which it adhered. It was determined to sweep half of it dry, and half after proper watering. This was done, and the sweepings removed were washed, to separate the refuse from the stony matter mingled with it. One third part of that which was taken dry, consisted of coarse grit, which would have been useful on the road-one-twelfth part only of that which was removed in the form of slop was stony matter; and that was so completely pulverized, as to be of scarcely any use; it had done its work. After the two portions of the road had been cleansed, the difference between them was very striking. That which was swept dry was still covered with adhesive matter, which was lifted by the wheels, together with the stones to which it adhered, the whole road being rough and uneven; the portion which had been swept with water was perfectly even and smooth. On the 24th both portions were swept, but only one quarter as much dirt was taken from that which had been water-swept as from the other. On the 26th it rained, and three times as much slop was taken off the part of the road which had not been waterswept on the 22nd. The preservative effect of water machine sweeping was most evident by the decidedly better condition of that portion of the road cleansed in this effective manner. The great objection urged against macadamized roads for streets is the annoyance by dust and dirt which they occasion, and many persons prefer submitting to the deafening noise of pavement in order to avoid these; but this would not be the case if water and machine-cleansing was adopted, the cost of which would be saved in dimi nished wear and tear. The entire cost of cleansing and watering Birmingham is about 5,000l. per annum, or less than one penny per week for each of its inhabitants. It has been objected to macadamized roads that the draught upon them is heavier than upon pavement ;-and with carriages altogether similar this is the case, and especially so with vehicles travelling slowly. But it must be remembered that the proportion of the draught is only one of the circumstances by which the labour of the horse is to be estimated. Another very important consideration is the surface which gives the horse the safest footing; and his footing on pavement is so much less secure than upon a good broken stone road, that he does not receive the full advantage of the smaller draught. Again, carriages-especially those travelling

quickly are exposed to much more violent concussions upon pavement than upon a smooth macadamized road; consequently, not only must the carriages be stronger, and therefore heavier, but the increased frequency and violence of the concussions consume a larger portion of power, which goes far to counterbalance the diminished friction. There can be no doubt that the wear and tear of both horses and vehicles is far greater upon pavement than upon macadamized roads. In reckoning the real cost of a road, all expenses attending its use should be calculated; and if this were done, pavement would be perceived to be exceedingly expensive. Carriages roll so smoothly over a well-maintained macadamized road, and horses are so little injured either by falls or strains, that I conceive the wear and tear upon them is not half of what it is on pavement.

SIR

SAMUEL BENTHAM'S VERMICULAR BARGES-INDIAN STEAM NAVIGATION.

Sir,-On reference to the Mechanics' Magazine, No. 1362, it may be observed that the articulation of Mr. Bourne's barges for East India navigation, their shallow draught of water, and the application of wheels to them, are so analogous to similar particulars of Sir Samuel Bentham's vermicular vessels, and his amphibious carriages, as to have led to the supposition that the articles in the Mechanics' Magazine respecting these inventions, had suggested the adaptation of similar contrivances to the navigation of East India rivers; but Mr. Jackson explicitly states that Mr. Bourne was altogether unacquainted with those inventions of Sir Samuel's. This therefore shows how true was an observation made in No. 1338 of the Mechanics' Magazine. In speaking of the Pentonville Penitentiary there was occasion to say, that "the seats for the prisoners when present at Divine service are constructed precisely in the same manner as they were designed" (by Sir Samuel for the intended Panopticon Chapel, 1793") and in the note, p. 298, it was observed, that "when two men of ability have it in view to produce the same effect, they frequently invent identical means of effecting their purpose. The seats and screens for the prisoners are similar to those invented by Sir Samuel, of which a drawing made in the year 1793, still exists." "Yet there is no reason to suppose that Colonel Jebb

ever saw those drawings." So it appears that Mr. Bourne and Sir Samuel have invented, separately, the same means for navigating shallow tortuous rivers.

The success with which Sir Samuel's vessels were attended, is confirmatory of Mr. Bourne's views, as exhibited in his published Report. But it may be asked, -If articulated shallow trains were so advantageous, why has their use not been continued in Russia? Sir Samuel immediately after their construction was selected to create and arm a flotilla at Cherson, and then to command the first division of it in the Liman of Otchahoff, where in three days' engagements his flotilla overthrew a more numerous Turkish one, took one ship of the line, sank another, and burnt seven more; his promotion for this service, and selection of a command in Siberia, entirely precluded further attention to the vermicular vessels. Lord St. Helen's and the Count de Segur (both of them in the year 1787, Ambassadors from their respective Courts to that of St. Petersburgh), having been on board of the Imperial Vermicular, had at different times before their death spoken in my presence of her; and it is to be regretted that no record has been preserved of details that from time to time have been elicited respecting the advantages of Sir Samuel's reticulated vessels, as such particulars would have tended to confirm the eligibility of Mr. Bourne's trains, navigated as they would be by steam power.

M. S. B.

THE LINES OF THE "CANOPUS." Sir, It is stated at p. 177, of your present volume, (see diagram, fig. 9,) that the breadth of Canopus at ss, lowest section near the keel, is a shade less than at A B, the surface or load water-line; in other words, that she is a straight wallsided ship below the water surface, like an old Indiaman.

Many years ago I saw the Canopus in dock at Plymouth, and my recollection is distinct that she had a well-defined French bottom. The flat floor of such vessels seldom exceeds half their main breadth, and there is commonly a quick curve at the junction of the floors and timbers with a regular curve to the

* See United Service Journal, 1829, pa t 2, p. 333.

surface of the water. On the contrary, in heavy ships of war the old English form of midship section had a much broader flat floor, about three-fourths of the main breadth with a quick curve below, and less curved sides to the load waterline.

If my views are correct the breadth of Canopus at s. s, would not exceed, perhaps not quite amount to, 40 feet, (see section 9). Small diagrams are apt to mislead; but as truth is a public object, perhaps your correspondent would be kind enough to state in figures the depth below load water-line of the several sections, ab, ss, &c., &c., and also whether Canopus has the French or old English midship section.

Sir W. Symonds's vessels are usually constructed with a straight rise of floor, and a quick curve just below the surface of water, and not with the curved floor of the diagram, and the small amount of breadth, 46 feet, a b, which requires confirmation-or rather the depth below surface; so that any person may lay a larger scale as the midship section required. I remain, your obedient servant, September 12, 1849.

MECHANICAL REVIVALS.

Z.

The newspapers of the past weekthe Times leading the way-have called in a very prominent manner the attention of the public to two "new" and wonder-working inventions-the one a rotary engine, "the invention of Cap tain W. E. Fitzmaurice, late of the 2nd Life-Guards, and his brother-in-law, Mr. Halford," the other a patent steamgenerator," invented" by a Mr. Wright.

The rotary engine has been reclaimed in the Times by the ingenious Mr. Elijah Galloway, C.E., as being the identical rotary engine last patented by him (December 14, 1846), and in which he has merely given Captain Fitzmaurice a proprietary interest for certain moneys had and received. The newspaper paragraphs mentioned that the Captain had (much to his honour!) 66 given the invention freely to the public." A smart way this of achieving eminence as an original inventor and public benefactor!

Mr. Wright's steam-generator is, in like manner, nothing more nor less than

the cellular steam-generator of Mr. W. H. James, the clever son of the clever but sadly ill-requited JAMES, to whom, more than any other man, belongs the merit of having originated the modern railway system, (see Mech. Mag., vol. xlix., pp. 401-500,) which cellular generator was patented years ago by Mr. James, and fully described in this Journal (vol. xlviii., p. 471). Mr. Wright's right to identify himself with this invention is just no right at all; or, at best, some such parchment or paper title, as that which Messrs. Fitzmaurice and Halford may, but do not boast of.

We must not, however, allow the false colours under which these Revivers spread their canvass to the wind, to prevent us from recording what the two inventions referred to, are stated to have accomplished in their resuscitated state.

Of the rotary engine we have this

account :

It was fitted up in a frigate's pinnace, 10 tons burden, carrying 5 tons, and though calculated at 10-horse power, occupied only 21 by 7 inches. The boat is 32 feet long and 8 feet broad in the beam, and though intended to mount carronades and carry men, was not fitted for speed; she is propelled by a screw, 3 feet diameter, worked by the engine, which made 200 revolutions per minute, and the boat 2 miles in 20 minutes, or 3 miles per hour. The working parts of the engine are most simple, consisting only of two pieces, which work with the greatest ease, are free from any dead points, and without the slightest vibration, however high ing; and the motion being a rolling one, the velocity. There are no springs or pack

there is little friction, and the works will last a great length of time without repair. It weighs less than 1 cwt. per horse power, and requires much less fuel than other engines. The boat started against the stream with seven persons on board in fine style, and on Mr. F. P. Smith timing the revolutions of the screw, he found them to be 192 per minute, and that may be considered the average speed on this occasion, with a very little exception, when the screw got entangled in weeds, which were soon removed when found adhering, by a few back turns of the screw. The distance run out and back was about 26 miles, and once through the lock of a canal; for which species of navigation it appears to be admirably adapted, having shown on a previous occasion its capabilities for towing, by drawing a broad-bowed and flat-bottomed barge, 30 feet long by 12 feet in breadth, at

the rate of three miles an hour against the stream. The speed attained by the boat on this occasion was ascertained by Mr. F. P. Smith and Captain Houston Stewart to be fully seven knots per hour, or 8.055 statute miles an hour-a remarkable result, con-. sidering that the boat was in no way constructed for speed. The ease with which the engine could be set in motion, and stopped or graduated to any degree of velocity up to its full speed, was a subject of surprise to the visitors, and the rough manner in which it was used to show its instantaneous effect, and difficulty to put it out of working order, could not be credited unless they were witnessed. The absence of vibration in the engine, and the uniform continuous motion, satisfied the visitors that Captain Fitzmaurice had overcome the difficulties which eminent engineers have always considered it difficult to obviate in rotary engines, and they left, on their return to town, much gratified with the result of all they had witnessed, and pleased with the minute details he entered into, when showing the model, and explaining the principle on which the two pieces of which it consists work, the one within the other. - Daily Journals.

The experiments with Mr. James's cellular steam-generator were as follows:

As

The experiments gave an evaporation of 12 lbs. of water by the combustion of 1 lb. of coal-that obtained by the usual construction of boilers not exceeding 8 lbs., or an increase, by the application of the patent, of 60 per cent. of evaporative power. Besides the saving of fuel thus to be effected, there is the advantage that the flame scarcely impinges on the boiler, arising from the intervention of the cellular vessel; and the boiler is accordingly saved from the rapid deterioration to which it is now exposed by the excessive heat which plays upon it. applied to steam navigation, the effect of so reduced a consumption of coal in the working of large steam-vessels, must be obvious; -the saving, in the shape of 50 to 60 per cent. in the article of fuel, being further increased by the extra space rendered available for the stowage of freight, or, on the other hand, the accelerated speed in steam propulsion, arising from a lightened burden of coal, are all advantages, the vital importance of which it is almost supererogatory to notice.

59 m. P.M., or 1 h. 12 m. from the commencement of the experiment, the indications of the water-gauge were taken, from which it appeared that, in that period of time, the apparatus had vaporised 720 lbs. of water, equal to 12.86 lbs. of water converted into steam by 1 lb. of coal. The general size of the boiler, which is of the wagon form, without a flue, is 6 ft. 9 in. long, 3 ft. 6 in. wide, and 2 ft. 6 in. high; the area of the bottom is about 21 superficial feet. The flue-surface is about 23 feet area. The area of the cellular plates exposed to the direct action of the fire is about 25 feet, and that of the plates within the boiler about 23 feet. The fire-bar surface is equal to 4 square feet. The quantity of water in the boiler was about 1500 lbs., and that contained in the cellular vessels about seven gallons. The quantity of water said to be evaporated by this boiler is about 12 cubic feet per hour, making it capable of raising steam sufficient for a 12-horse power engine, although its dimensions are only equal to that of an ordinary 4-horse power boiler.

It may be observed, as relates to the economy calculated upon by the application of the patent to steam navigation, to say nothing of the saving of space, that, taking a vessel of 400-horse power, such is found to consume about 27 tons of coal per day of 24 hours, which, with a saving of 60 per cent., assuming the passage to be 15 days, would give the following results :-Consumption of coal, say, 400 tons, saving 240 tons, which, if taken at 40s. per ton, including the cost of coals and allowance for space occupied, and which might otherwise be applied, would give a saving of 4801. We are aware that an estimate has been made, whereby our assumed saving is carried out more than threefold on a voyage of 45 days; but we think the present statement amply sufficient to establish the saving which may be effected.

As applied to locomotive engines, it is to be supposed the patent will be equally applicable, although we are well aware that difficulties present themselves which do not apply to stationary engines, or those employed for steam navigation. The cost of coke per mile is, however, so formidable an item, that any saving which could be effected would necessarily lead to a considerable increase of profit and dividends to the shareholders. We do not deem it necessary further to enter on the varied applications, such as breweries, distilleries, and other establishments, where large quantities of liquid are required to be boiled, heated, or converted into steam, as the excess of power obtained is equally applicable, and a com

parative saving consequently effected.-Mining Journal.

REPORT OF THE COMMISSIONER OF PATENTS OF THE UNITED STATES ON EXPLOSIONS

OF STEAM BOILERS, DECEMBER 30, 1848.

(Continued from page 262.)

That "undue pressure within a boiler, gradually increased," is one of the most frequent causes of explosions, has been proved, as well by recorded cases as by the experiments of the committee. One of the points of inquiry to which their attention was specially directed, was to ascertain the sort of bursting produced by a gradual increase of pressure; and after several decisive experiments, they came to the conclusion that all the circumstances attending the most violent explosions may occur without a sudden increase of pressure within a boiler. This gradually increased pressure may result from the accidental failure of the apparatus intended to relieve it, or from this being intentionally prevented from operating by the reckless hands which sometimes have the control of it. Of the ninety-eight cases in which the causes of explosions are stated in the returns herewith submitted, sixteen (being 16 per cent. of the whole), are assigned to this cause. The term " excessive pressure" in the Table indicates these cases.

The cases referred to "the presence of unduly heated metal within the boiler," are also sixteen. The danger attending the overheating of the boiler arises from the diminished tenacity of the metal thereby produced, which renders it incapable of any longer sustaining the ordinary working pressure; and from the metal's being made itself a reservoir of heat, capable of generating an increased quantity of highly elastic steam, as soon as water shall be brought in contact with it. This overheating of the boiler may be occasioned by suffering the water to become too low, or by allowing sediment to accumulate on the bottom. The former cause operates by exposing a portion of the surface next the fire to the action of heat while uncovered by water, and the latter by interposing a medium of but low conducting power between the fire and the water, thereby suffering the metal to acquire heat faster than that heat can be conveyed to the water. In either case the metal is technically said to be "burnt," and even if no serious consequences should occur at the time when such burning takes place, still the tenacity of the metal is thereby permanently dimi

* Frank. Jour., vol. xvii., p. 225.

nished, its thickness decreased, and the liability to explosion, therefore, greatly enhanced. In boilers where flues are employed, their collapse is the ordinary result of this state of things.

The deficiency of water may be the consequence of the pumps being obstructed, so as to throw in less than the requisite supply; or from their being heated, so as to inject steam; or from their not being in action when the engine is stopped and steam blowing off. The sudden removal of these causes of deficient supply, while the intensity of the fire continues at the same time undiminished, is very likely to produce an explosion for reasons already explained. Hence the greater number of these accidents which occur immediately upon starting the engine after a stopping at a landing, or for repairs. Mr. Evans expresses the opinion, that "eight out of ten explosions take place just at the time of starting from a landing, the engine making generally but one or two revolutions."+

The subject of deposits, in connexion with the overheating of the metal of the boiler, is one of great importance, and one which is still comparatively open as a field of research. The Franklin Committee made it one point of their inquiry to ascertain by experiment the effect of deposits in boilers. They admitted the collection and hardening of such deposits on the bottom of the boiler, and attributed the danger from them to the production of exfoliations of oxide, which gradually reduced the thickness of the metal, or to the weakening increase of temperature in the metal which they permit.‡

With regard to incrustations and deposites in the interior of steam boilers, it may in general be admitted that these must differ with the character of the water used. In boilers using "hard" water, they consist chiefly of the carbonates of lime and iron mixed with oxide of iron; containing, besides, the earthy salts from the water. Boilers using ocean water are found to detect the differences existing in different parts of the ocean in regard to the composition of its water. It appears that certain "scales" which were taken from the boilers of the United States steamer Marcy, and subjected to analysis by Professor Johnson, were found to collect in the boilers while running over the Bahama Banks; and the experience of the Marcy is confirmed by that of other steamers which have traversed the same