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buried deeper, compensates for this want of resistance.

10. With side wheels, sails and steam are rarely or never employed in conjunction with advantage, because, if the wind is on the side, sails heel the vessel more, bury the lee wheel, and lift the weather one; under which circumstances, both act disadvantageously, and produce less speed, or certainly no more than would result from the sails alone, or from steam alone. The case before the wind might not be much if any better. With a fair wind, therefore, a ship may go equally fast with sails alone, or steam alone, or with sails and steam in conjunction. But if sails are used, the steam cannot be dispensed with, unless the wheels are "disconnected," so that they shall afford no obstruction to the progress of the vessel whilst the engines

are at rest.

11. There are two methods practised of disconnecting. One is to unstrap the connecting rod from the crank pin, and let the crank and wheel revolve independently of the engine; the other is to take off a third of the paddle boards from the arms of the wheel, and confine the wheels with the naked arms in the water, which present a very small obstruction. To perform either of these operations, it is necessary perfectly to confine the wheels by ropes and chains, which, when there is a sea on, it is difficult or impossible to accomplish.

This difficulty of disconnecting a side wheel, or of connecting again at pleasure in an emergency in any weather, is the principal obstruction to the introduction of steam power as an auxiliary on board sailing vessels. Persons feeling the uncertainty of being able to reconnect, hesitate to disconnect, and therefore employ steam, at great expense of fuel, when, but for this difficulty and uncertainty, they would more frequently employ sails, and obtain equal or superior speed. If side paddles are adhered to in sailing ships, some arrangement, strong, simple, and easy of adjustment for connecting and disconnecting the wheels and engines, is indispensable, and invites the ingenuity of those engaged in the mechanic arts.

Submerged Propellers.

12. A principal advantage of submerged propellers, is, that their paddles being beneath the action of the sea, are with ease disconnected, even in the roughest weather; and the uncertainty existing in that respect with side wheels is obviated. Consequently vessels fitted with propellers may sail more and steam less,-steaming only in head winds, calms, or emergencies.

Another advantage which submerged pro

pellers present in ocean navigation is, that they are not thrown out of water by heel of the vessel under canvas; and therefore, with them, both sails and steam may act in conjunction, with great advantage and economy.

13. In favour of the propellers it may be further urged, that they are not affected by the more or less deeply laden state of a vessel with coal, which, when leaving port, dips side wheels so much that power is lost, and on arriving at port dips them so lightly as to produce also from that cause great loss of power. Also that they are protected from shot and other dangers at the surface.

Against the propellers it may be urged, that they are inacessible for repairs, in case of derangement, without going into docks, which are rarely at hand. A loss of power is generally attributed to them, as compared with side wheels in smooth water. Possibly propellers now in use may be rendered accessible by devices that will obviate the necessity of docking; and other arrangements may be presented, free from these objections. At all events, it may safely be predicted that steam navigation will soon become common on the ocean, as auxiliary to sails, and that this result will be accomplished by means of propellers, and propellers only.

LAWS OF FALLING BODIES.

Sir,-Your correspondent, Mr. Davison, whose communication on the laws of falling bodies you have printed in No. 1162, has fallen into some curious mistakes, which he will, perhaps, be obliged to me for pointing out.

1. He says, "We are at liberty to institute a comparison between the sagittæ of two arcs described in the same time without any regard to their size," &c.

This is not the case. The sagittæ are only measures of the central forces when the arcs are so small that the direction and magnitude of the forces may be considered as constant during the time of describing the arcs.

2. He seems to make a double mistake as to the meaning of the law of the equable description of areas, for he applies it to compare the periods of revolution of two bodies describing different orbits, when the law only applies to the times of the same body describing different portions of its orbit. He also seems to confound areas with arcs, for he says that the proportion of the area A EC to the area A B C, when S E is diminished,

в в 2

becomes ultimately as A C to ABC; whereas, in truth, the area A EC becomes ultimately infinitely small; and his reasoning ought to have led him to the absurd result that a body descending to a centre of force in a right line would reach the centre in an infinitely short space of time.

3. Mr. Davison is, of course, right, in saying that if the force of projection is less than that in a circle, the body projected will describe an ellipse which will fall within the circle, but both his figure and his reasoning assume that the centre of force will be in the centre of the ellipse, whereas it will be in the further focus; and when the force of projection becomes very small, the body will descend nearly in a straight line to the centre, and turn sharp round and re-ascend to its original position.

4. The mistake just mentioned is the occasion of Mr. Davison's making the further mistake of supposing that according to Newton's theory the time of falling to the centre from a given distance is

one

e-fourth of the periodic time of a body moving in a circle at the same distance; whereas it is obviously one-half the periodic time of a body describing a circle at one-half the distance, which time or less than the other in the proportion of 1 to 2

5. Mr. Davison makes another mistake, in supposing that "by mechanics a body descending from any height will go over the same space in half the time with the velocity acquired at the end of the fall." This is only true where the force that acts is constant, not where it varies with the position of the falling body, as would be the case with a body falling from the moon to the earth.

Mr. Davison appears, and most laudably, no doubt, to have endeavoured to obtain some knowledge of the results of Newton's theory applied to the motions of the planets, without having the opportunity or the ability to make himself master of the means by which these results are obtained. If such be the case he will, I think, find in the article " Gravitation," in the Penny Cyclopædia, written by the Astronomer Royal, and also published separately, an explanation of the mode of action of gravity which an acute personl but who has not the use of mathematica, tools, may probably understand and apply with less chance of falling into gross

We have lately bad our attention invited to the singular appearance now worn by the planet Mars. Hitherto, this planet has been distinguished by a fiery redness of colour; which, to use the language of Sir John Herschell, "indicates an ochrey tinge in the general soil, like what the red sandstone districts of the earth may possibly offer to the inhabitants of Mars." Such is, however, no longer the case; that planet having lost all appearance of redness, and put on a brilliant white aspect, vying in applanet Jupiter itself. parent magnitude and brightness with the The only changes

which have heretofore been noticed in Mars, are those, the knowledge of which was derived from observations with the large reflecting telescopes of Herschell. These telescopes exhibit the appearance of brilliant white spots at the poles; which spots, from the circumstance of their always becoming visible in winter, and disappearing as the poles advanced towards their summer position, have reasonably been attributed to the presence of snow. The novel appearance now described to us, however, by the Hon. Company's astronomer, Mr. Taylor, is such as that the whole of the planet, with the exception of a moderately broad equatorial belt, assumes a decidedly white aspect, strongly contrasting with what he has ever before noticed. We look forward with great anxiety and interest to those observations on the above planet which may be expected to have been made, through the medium of the numerous and powerful telescopes now at work in Europe. Lord Rosse's magnificent telescope will likewise (we venture to hope) have been perfected, so as to allow of his bringing it to bear upon the celestial body apparently undergoing the remarkable change discerned by Mr. Taylor; and, for the benefit of those who do not enjoy the opportunity of looking through any large and powerful instrument, we confidently trust that the labours of the artist and engraver will be put in requisition, with a view of making them acquainted with these wonders of the heavens.-Madras Spectator.

hulk, opposite to the dockyard, having been towed up on Friday, the 21st inst., by the Wildfire steam vessel, she having broken down at sea. This unfortunate vessel, it appears, left Cockham-wood Reach at twelve o'clock at noon, on Wednesday, the 18th inst., as reported, for Portsmouth, whereas she was to take a cruise in the Channel, having on board Captain W. H. Shirreff, R.N., Captain Superintendent of her Majesty's yard, accompanied by Vice-Admiral the Earl of Dundonald, the constructor of her engines, and manned by the seamen of the ordinary; and reached Sheerness in about two hours and a half, the paddle wheels revolving about thirteen times to the minute, and on her arrival outside the river, touching the sea-water, her pace became slackened, and it gradually decreased, and on her arrival near the Mouse, her speed was so reduced that her wheels only made eleven revolutions in the minute, although she had a strong wind in her favour, and, in attempting to turn her, she drifted astern; consequently it was found necessary to anchor her for the night, as it was rough, and blew a strong gale. The next morning the engineers could not get the wheels to turn until noon, when they revolved about five times to the minute, and at which rate the engines continued working until eight o'clock at night. The next morning (Thursday), the weather being fine, it was attempted to run the vessel over to the Downs, but it was found that, by using every exertion, she would not make head against the sea. Further trial was therefore deemed useless, and the vessel was beat up again for Sheerness; and on her arrival in the river water she returned to her former speed. On passing her Majesty's vessel Trafalgar, however, her engines broke down, and she was obliged to anchor for the night; and on Friday she was towed to this port. On raising her anchor it struck her bow, and made a hole in it. It is now clear that this vessel, according to her present construction, will never go a-head, having now failed in a hundred experiments, and having had all the resources of Chathamyard lavishly expended on her for the last year, without the least improvement. Her engine is stated to be very defective. The rotary engine of this vessel, it appears, is fitted with four tubular boilers, equal in bulk and expenditure of fuel to 500-horse power boilers, and with engines estimated at 220-horse power, but withal, the boilers have never worked up to 60-horse power. The boilers are divided into two sets, with a stokehole between them, which forms a kind of pandemonium, where the unfortunate firemen are scorched by six furnaces on each side of them, and by the cylinders full of

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steam above their heads, while their feet and ankles are immersed in hot water, and where they are deprived alike of air and light. It is stated that this machinery is not fitted with the appendages which experience has shown to be essential to the safety of a steamvessel, because they cannot be attached to a rotary engine without extraordinary complication. Yet, notwithstanding these omissions, it occupies 38 feet fore and aft, and great part of the upper deck; while a perfect pair of engines of 200-horse power, with tubular boilers, and every appendage for safety and convenience complete, with ample airy stokehole, and free access to every part, would not occupy more than 34 feet.

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During all the expensive experiments on this unfortunate craft not the least improvement has been made. With wheels proportioned to her nominal power, she would not make two miles an hour, and when sent to sea in this instance she did not make headway against a light sea, whereas another vessel would have run full speed.

"The Janus, on going out, had only forty tons of coals and four tuns of water on board. She is now two feet lighter than she was during her first trips, and has one and a half-streak of her copper painted black, to make her appear deep in the water. engines, since her arrival, are being taken to pieces."-Times Correspondent.

Her

To the Editor of the "Times." Sir, The various short paragraphs respecting the Janus and her engines which have found their way to the public through your widely-circulated paper, having appeared to me to proceed from uninformed persons, I have abstained from troubling you to correct errors; but perceiving that nearly half a column has this day been devoted to the subject, and that an insidious misrepresentation has been transmitted to you, which may impose on the public, I claim of your justice a space sufficient to rectify erroneous assertions, and to place the forbearance of the Admiralty, wisely shown towards the developement of a machine (peculiarly adapted to actuate the screw propeller) free from exposure to derangement by shot, which is of the highest importance to the naval service. I am, Sir, your obedient servant, DUNDONALD.

8, Chesterfield-street, Nov. 26.

Memoranda, being Facts relative to the Progress and Performance of the Revolving Engine on the Principle of those in her Majesty's Sloop Janus.

The Earl of Minto, when First Lord of the Admiralty, having learned from his bro

ther, Rear-Admiral Elliott, that rotatory engines had been successfully used (in two small steam-boats), and that their compactness, levity, and celerity of motion rendered that kind of engine peculiarly suited to the naval service, ordered a trial to be made of the power of a condensing engine on that principle by pumping water from a well in Portsmouth Dockyard.

This engine had been at work for full twelve months when the present Admiralty made their first official visit to that yard, and their Lordships had an opportunity of witnessing the energy and power it then displayed, which, by constant work, has now increased to such a degree, that not one of the thirteen engines in the yard (most of which are on Watt's principle) has produced a better vacuum, or required less repair, as is testified by Mr. Taplin, the chief engineer and mechanist of that yard.

This result was not, however, obtained without great anxiety and trouble. Thirty times at least within 18 months of its erection was this engine taken to pieces, and at times parts of it were sent to London to be altered, under the impression that some defect or other prevented its efficient performance. Such, indeed, was the prejudice originally existing, augmented by repeated failures to work the engine, that it was on the point of being finally rejected by the authorities, when it occurred that perhaps the cold water pipe leading to the condenser might be choked. Admiral Sir Edward Codrington, Rear Admiral Bouverie, Captain Sir Thomas Hastings, Mr. Taplin, and Mr. Blake, the master shipbuilder, 'were present to witness the result of, perhaps, the last trial; and they and others saw the injection.. pipe cut, and a plug of wood withdrawn, which blocked the passage, so that not onefourth of the water required could enter the condenser; indeed, after the pipe was rejoined on the following day, the engine could scarcely work two of the three pumps it was destined to put in motion; it was therefore again pulled to pieces, and also the air pump (which had never before been suspected as a cause of obstruction); nevertheless it was found that the delivery valve was not only open, but was retained open by its cover being screwed down upon it, thereby effectually preventing the formation of a vacuum, even by the most free introduction of injection water, and the most complete condensation.

It may here be noticed that a ball of rope yarn and a hank of strands were subsequently extracted from the injection-pipe; and that within the last two months, on examining the lower valve water-pumps at the bottom of the well, in the middle suction-pipe a plug of

It need, therefore, be no matter of surprise if the large engines of the Janus have been delayed in the performance of their duty, or that numerous trials failed to produce a satisfactory result. On Saturday, the 15th, however, the engines started well, and were accelerating, when the wedges of the clutches of the paddle-wheels (being slackly driven) slipped, and the engine flew round and broke the chain of the air-pump, which being repaired on Monday, the Janus proceeded down the Medway purposely at a moderate rate, in order to ascertain if any damage had been done to the engines themselves by the accident of Saturday. There being no visible indication of derangement, the vessel proceeded, and was anchored near the Mouse Light at dusk, on account of the difficulty of passing through the shoals at night. On the following morning on setting the engines to work, no vacuum could be formed in one engine, which having thrown the whole labour on the other, it soon became manifest that some partial derangement had taken place therein; and a search having been made, it was discovered that one of the snift valves had been misplaced since the preceding evening; consequently the atmospheric air had thereby free access to the condenser. This impediment having been detected and removed, it was further discovered that the end plate of the air-pump (lately withdrawn for inspection) had been improperly jointed, so as to suspend its useful action. Every person conversant with the mechanism of engines will fully understand how totally independ ent these impediments are of the principle of the engine, yet how fatal to its operations, which I have no doubt, like the Portsmouth engine, will be rendered perfectly efficient. Indeed, the brief specimen exhibited on Saturday confirms this opinion, having accelerated from 18 to upwards of 20 revolutions before the accident.

With regard to the boilers of the Janus, it is hereby fearlessly asserted, that having been first tested by authority of the Admi ralty, under the immediate inspection of the officers of Chatham-yard, and the greatly superior evaporative power having been doubted, an application was made to the Admiralty to direct the engineer department of Woolwich Dockyard to test the boilers. The

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result was that their power amounted to 314 cubic feet of water evaporated per hour, at the economical rate of 12.9 pounds, by each pound of Llangenneck coal-a result testified by the engineer's official report of the trial, now in the records of the Admiralty, dated the 19th of last November; the importance of which result, in a maritime point of view, every person acquainted with steam navigation is competent to appreciate. Lastly, in regard to the temperature of the "stoke-hole," although the furnaces are opposite, it may be truly asserted, that the temperature is less than at the same distance from any tubular boilers in her Majesty's service.

DUNDONALD.

UNDERHAY'S PATENT IMPROVEMENTS IN
VALVES AND TAPS.
[Patent dated 3rd May, 1845; Specification enrolled
Nov. 3, 1845.]

The present patent comprehends first, certain improvements in ball valve cocks, and second, a new description of valves, to which the inventor gives the name of cam valves."

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The common ball-cock, as all practical men are well aware, is extremely liable to get out of order, either through turning hard or leaking. The water-way, through the barrel and key of the square cocks (as they are technically terméd) way is contracted to about one-third the area of the pipe; when those again with round or full water-ways are used, the barrel and key are necessarily much increased in size, and a larger and heavier ball is required to open and shut them. Another objection to the latter is, that they close or open the passage very slowly, the ball having of course to describe the fourth part of a circle, (the radius being the length of the ball and rod.) Many attempts have been made to overcome these objections, but hitherto with doubtful success. Mr. Underhay's plan for the purpose is represented in the following figure; it is simple and ingenious, and appears to us likely to act most effectively.

A is the elbow-piece of the supplypipe, through which the water or other fluid is to flow into a vessel to a height to be regulated by the rise of the ball or float B (not shown in the figure.) C is a valve-box which is screwed on to the end of the supply-pipe A, and terminates at bottom in a bearing-piece D, having two dependent arms of unequal length, a b.

The lever E of the ball B is passed through a slot in the long arm a, of the valve-box, and secured at its extreme end in an open cleft in the short arm b, by means of a cross pin c, which passes through the cheeks of the cleft and the interposed end of the lever, and on which pin the lever turns freely. The length of the slot in the arm a determines, of course, the of action allowed to the range lever E; F is the valve, which consists of a portion of a metallic cone c, which fits into a conical recess d, in the mouth of the elbow-piece A of the supply-pipe; and is the spindle, which passes down through a pipe f, supported by a crossbearing, g, in the centre of the valve-box C. As long as the water or other fluid is at so low a level as not to act on and raise the ball, the spindle of the valve rests on the lever E, as shown in fig. 1, and the water or other fluid flows freely in all around; but as soon as the rise of the water raises the ball, it raises in a like degree the lever attached to the ball, and with it the spindle of the valve F; and so the action continues till the lever E attains a position exactly parallel with the valve F, (as indicated by the dotted lines in fig. 1,) and that valve closes the mouth of the supply-pipe, and prevents the ingress of any more water or other fluid. And by an inverse course of action, as soon as the water or other fluid begins to fall below the required height, and the ball or float to fall along with it, an opening is made for a fresh supply.

It will be observed of this ball, 1st,