Of

exclusive of government vessels. these 600, there are only 39 in all the colonies and possessions, which contain an aggregate population six or seven times larger than the mother country. Is the monstrous flotilla of five steam vessels in the East Indies at all con mensurate with the wants of the populat or proportioned to the importance out, part of our dominions?

Since my first letter referring to the want of steamers in the East Indies, and the tardy stinted compliance with the reasonable claims of the British residents there, upon the merchant-princes in Leadenhall-street, I am informed, that two other steam. vessels have been contracted for, to be built in England, which will probably arrive out at the end of 1839, or during the early part of 1840, and add to our numerous and efficient steam flotilla already existing in the East Indies.

As an illustration of the greater velocity acquired by large vessels over smaller ones of the same form and proportions, I will just mention, that by advice from the British Queen off Falmouth, she was going through the water at the rate of eight knots, with a light breeze. This

circumstance justifies the general expectation that she will prove a very fast vessel when steaming, if her machinery be properly adapted for her, and is equal to its reputed power.

Apologizing for having trespassed so much with a subject which cannot but interest your readers, I take leave of the controversy, and subscribe myself, Your obedient servant,

July 10, 1838.

GEORGE BAYLEY.

STEAM-BOILER EXPLOSIONS--THEORY

AND PRACTICE.

Sir,-Your correspondent "Scrutator" has assigned a probable, and certainly most efficient, cause for the bursting of the Victoria's boiler, or more properly the collapse of the internal flue,-the manner in which similar boilers, containing high steam, nine times out of ten, explode.

The steam-room in cylindrical boilers with a large flue is, proportionally to the water space, much less than in rectangular boilers,-a defect which must be met, either by an increased steam-chest or pipe, or by keeping the steam higher in

the boiler, and throttling it down into the cylinder. My object, however, is to point out, that the connection of scientific and practical knowledge is alone of value.

The practical man will blunder on till he is right at last, if he has common sense and sufficient funds. Theorists are equally subject to blunders, to the great delight of the practicists-parties, by the bye, who are often alone in possession of correct data, and who, by experience derived from observation, are enabled to guess at, rather than to exhibit reasoning for probable results, under different conditions-theorists, in fact, without a language to express their ideas. This, and the limits of power and correction, under different conditions, so as to lead to the highest possible results by the shortest path, are the legitimate objects of theory. Another class are sometimes called theorists in contempt,-persons not more remarkable for their reckless assertions without proof, than the absence of both practical and scientific knowledge." Scrutator" very properly objects to "if's" and "but's," "-conditions, in fact, not clearly expressed-loopholes for erroneous opinions,-and gives an example of their misuse in his own letter: "This boiler would do well at sea, if external condensation was adopted." What has the boiler to do with the means employed by the engineer to produce an assigned vacuum, as long as that assigned vacuum is produced?* The boiler has only to perform its allotted task. If the meaning is that a better condensation is afforded, as its advocates assert, by external condensation-for instance, to the extent of one inch of mercury, then it amounts to an admission of inferiority, to be estimated on the principles of heat required to evaporate water at about 16 and 161⁄2 lbs. pressure respectively, into steam, as used in the cylinder.

Theoretical, like practical, opinions are sometimes at variance, and in such cases one at least of the theoretical opinions will be oftener traced to false, or

*We are surprised that our correspondent, who appears to understand his subject upon other points, should put such a question. The advantage of external condensation alluded to by "Scrutator" had no reference to the production of a vacuum, but to the condensing of the steam and the returning it in the form of pure water to the boiler, whereby tubes or small chambers may be used without their being liable to be choked up by the incrustations of saline or other deposits incident to the use of sea water. -ED. M. M.

the omission of important, data, than to incorrect reasoning.

Success and failure were both theoreti cally predicted of the direct unknown voyage of the Great Western to New York, from arguments founded on known voyages performed; the failing theory has attracted most attention, like a bad hole in blasting rocks-much noise and no work. The successful theory is remarkably well expressed in a report to the committee at Bristol, dated January 1st, 1836, and signed Christopher Claxton, managing director, which silently effected its purpose. The pleasure I felt on reading this report, as given in the Nautical Magazine in January, 1837, was only equalled by a comparison of the estimated, with the actual results, of the first voyage.

Previous to the opening of the Manchester and Liverpool railway, theory arguing from known performances, foretold that a speed greater than ten or twelve miles per hour would be impracticable, and quite forgot a possible conditionincreased evaporation in the same space, without any great increase of boilerweight. The method of forming numerous flues of small tubes-the reverse of the common steam-coach boiler-seems to have been suggested by the treasurer -evidently a theorist respecting heatto the engineer, whose adoption of the plan is as creditable as the suggestion, and who fairly earned the competition and renown.

Theory, at least, did good service here, but sooner or later it would have been effected by some person, who might have had pretensions to have been dignified with the more coveted title of being a practical man.

If any difficulty was ever found to occur in not getting the lower tube to draw as much air as the upper, theory would suggest that a proportionate contraction of the upper flues at either end would effect this object. Practice might find out some objection relative to a soot deposit. I have alluded to this merely to show the connection between theory and practice without any knowledge whether it has ever been done, or required to have been done.

The theory of fusible plugs, to melt at assigned temperatures, is very pretty, and was introduced with Trevethick's high-pressure boilers, and is still often used in the mining modification of these boilers. Recent experiments have shown

that on continued heat they melt at lower temperatures; but for this allowance can be made. It was lately mentioned to me that these plugs have been abandoned in steamers, where they will not do, especially in the weather flues, which are apt to get hot when the vessel heels. This is a specimen of a practical argument from a defect, not of the plug, but of the boiler: they must meet the real objections how they can-fixing difficulties, and liability of failure on a lee shore.

For smooth water craft, partitions in a single boiler, with a separate feed-pipe to each division, will obviate the first objection; but the large boiler top is exceedingly objectionable to passengers, as on explosion the whole flies off together. It is their interest to have separate boilers-then the flues become the weakest parts, and the enginemen must keep a bright look-out for themselves, as the only persons likely to suffer on an explosion. Partitions are not sufficient in sea-going vessels to prevent, under some circumstances, the effect of the constant flush of the water to leeward. Three or four separate boilers alone will enable the weather-boiler to be forced, and the sea one eased, by which means a great increase of stability is afforded--a point of as much importance in crank steamers as trimming to windward in crank pleasure-boats.

Theory, judging from the disposition to obtain power in a small space, and the eventual tendency of expansion, at present only used with low steam, may safely predict the rapid approach of a most dangerous era in steam navigation, -the transition period from low to higher steam. Competition will induce the attempt, and (whether successful or not) considerable danger will exist, until the safety conditions are fully ascertained. As for the United States, they seem simply distinguished, in the inland waters especially, by an engineering recklessness, in utter defiance of theory and practice.

Legal enactments are likely to prove futile. Two points alone perhaps would prove efficient,-increase of knowledge among the enginemen, which time only can effect, and a deodand on the vessel for each death of 1007., to be doubled on neglect being proved, so as to render an explosion an expensive operation for the

owners.

I remain, Sir, yours respectfully,

N. S.

BADDELEY'S AND WHITE LAW'S PLAN

FOR FEEDING STEAM-BOILERS.

Sir, I am sorry that I should so grievously have roused the ire of Mr. James Whitelaw, by the opinion I entertain of his plan for feeding steamboilers, promulgated in your 769th Number. As I am by no means singular in my opinion, it is just possible that I may be right, and Mr. Whitelaw wrong. I would refer to "Nauticus's" letter at page 107, as the best answer that could be given to Mr. Whitelaw's epistle.

Mr. Whitelaw asks if I "know any thing of a Mr. Whitelaw who sent a drawing and description of two forms of a feeding apparatus to the Society of Arts, and who got a reward for his plan; one form of which is given in the volume of their Transactions published in 1833?"

gen

In reply, I know nothing of this tleman, but I have just procured a copy of the Society's Transactions for that period, from which I have extracted, verbatim, all the information relative to Mr. George Whitelaw's plan, which, in fairness to both the Messrs. Whitelaw, and in justice to myself, I send for insertion in your Magazine with this letter. With the form not published in the Society's Transactions, I am wholly unacquainted; but as Mr. James Whitelaw says it is exactly the same in principle and plan as the one I call mine, I take it for granted that it is so, with the difference mentioned by Mr. W.; but I presume the Society considered the plan they have published in their Transactions the best of the two. I candidly admit the identity of principle in Mr. G. Whitelaw's apparatus, with that which appeared as mine in your 572nd Number, and only beg to add, that at the very time Mr. Whitelaw was addressing his communication to the Society of Arts, I was exhibiting a working drawing of my plan at Birmingham and elsewhere, with a view to its being taken up and patented. Not succeeding in this object, I subsequently published a description of my plan in your 21st volume. So that, while I admit perfect originality both in plan and principle to Mr. Whitelaw, I likewise claim the same for myself. I cannot help adverting to the statement in Mr. Whitelaw's communication that water was supplied to steam-boilers through the agency of the engine-man alone!" whereas, a force-pump wrought by the

By comparing the arrangement given in No. 572, with that now extracted from the Society's Transactions, I think it will generally be conceded that the action of one slide-valve (for the second can be very advantageously dispensed with) is preferable to the revolving of a hollow stop-cock; especially if made large enough to hold twice the quantity of water required by the boiler during one revolution of the stopper. Although, as the stopper is made to revolve by connexion with the engine, by means of wheel-work, it seems strange that this size should be insisted upon as necessary.

The subject at present at issue, "the supply of water to steam-boilers" is most important; one, at this time, invested with solemn interest, and deserving the best attention of all, both as a matter of economy, and also as a preventive against those melancholy accidents, of late so lamentably frequent.

Any discussion, therefore, which brings into juxta-position the various plans proposed from time to time for attaining this object, cannot fail to prove useful. Whether the propounders are actuated by selfish and interested, or disinterested and benevolent motives, will signify but little facts, those "stubborn things," will speak for themselves, and by gathering a little from one and a little from another, practical men will soon obtain the means of effecting the object sought, with certainty, economy, and safety. I remain, Sir, yours respectfully, WILLIAM BADDELEY.

London, July 5, 1838.

"Method of Feeding a High-Pressure Boiler.

"Clasgow, May 5, 1833. "Sir, I take the liberty of forwarding to you, that you may lay before the Society for the Encouragement of Arts, &c., the drawings of a new method for regulating the supply of water in steam-boat and highpressure engine boilers. At present this is done through the agency of the engine-man alone, which is not only troublesome, but unsafe, as, from neglect or carelessness on his part, too much or too little water might be admitted into the boiler, so as in one case to be hurtful to the working of the engine, or in the other to endanger the

(as it may be named), the hollow part of the stopper would be required to contain full twice the quantity of water which the boiler would require during one revolution of the stopper. The pipe that leads to the hotwell should be made pretty wide, and the hot-well must be high enough, so that the water may run into the stopper of its own accord. The pipe for conducting the water from the hot-well must on no account have any bends in it turning downwards, as they would prevent the uncondensed steam, or air, that is displaced from the stopper, from escaping."-Transactions of the Society of Arts, &c., vol. 49, 1833.

"The plan consists merely of a common stop-cock, with the key or stopper made hollow, and open only on one side. Let the branch A be the one leading to the hot-well of the engine, and the branch B the one going to the boiler. The stopper can only communicate with one of these branches at a time. The rod C is for conveying a rotatory motion to the stopper from the engine. This may be easily done by means of wheel-work. The spiral spring D is for keeping the stopper in its place.*

"To explain its Action-Let the stopper be in the position shown in the diagram, that is, having its opening opposite the branch leading to the hot-well. In this case, the water from the hot-well would fill the hollow part of the stopper, and as the stopper would be revolving, the communication with the hot-well would come to be shut off, and the opening of the stopper to be opposite the branch B going to the boiler. This would allow the water in the stopper to pass into the boiler, till the water in the stopper came to a level with that in the boiler.

"The stopper again turning to the opposite side would receive another charge, and again deliver the proper quantity into the boiler. In constructing this feed-regulator

* How it fulfils this office is not very evident.W. B.

ON REVOLVING SLIDE-RESTS.

Sir, Mr. James Wilcox, whose revolving slide-rest forms the frontispiece to your 777th Number, will perhaps pardon me, when I state that his contrivance (evidently the production of an amateur) embodies nothing that is new, and little that is really useful. There is a want of firmness and stability, both in the plan and in the materials employed by Mr. Wilcox, that would render his apparatus wholly unfit for either large spheres, or hard materials; inasmuch as the smallest vibration would cause a serious deviation from truth. I strongly suspect the existence of several very beautiful tools of this description, but if so, the owners keep them so profoundly secret, as to render the fact very difficult of being ascertained with any degree of certainty.

Having lately invented a new manufacture, in which it became absolutely necessary to have the power of turning, both internally and externally, spheres of metal, of considerable size, with perfect accuracy, I have designed and executed a revolving slide-rest which performs this office with great facility. My rest combines all the powers of Mr. Wilcox's, with more besides, in a very convenient manner; it accomplishes what is required with astonishing precision, and will turn balls of any material from an eighth of an inch to four or more inches in diameter.

As the manufacture to which I have alluded is not yet made public, I cannot, without injury to the parties who are engaged in it, enter into a more minute explanation at present, but I hope shortly to be able to send you further parti

culars. In the mean time, if Mr. Wilcox will send to your office for a letter directed to him there, he will have the opportunity afforded him of obtaining more of the information he solicits than I can conveniently communicate "through the medium of your valuable Magazine.”` I remain, Sir, yours respectfully, WM. BADDELEY.

London, July 10, 1838.

THE BOOMARANG.

Sir, In a former Number of your Magazine I gave an account of the boomarang, a missile used by the natives of New Holland, in the hope that some scientific gentleman would be induced to examine the causes of its very singular gyrations when thrown into the air; but although I have read several explanations of the supposed causes, none of them appear conclusive. In my opinion, the best form to give the missile in order to cause it to return, is half, or something more than half a circle, it is difficult to find a piece of timber sufficiently strong to prevent breaking when cut into this form; the best part of a tree is the fork; that, for instance, of an old apple tree, the grain then runs somewhat circular. I have thrown two or three boomarangs at a time; they were made perfectly flat on each side in order to lie the better in my hand, when all have returned after going forward about fifty yards, giving me sufficient time to select and shoot at two of them with a double-barrel gun. This kind of practice would soon make a man a good flying shot;

I have tried various kinds of ballistas or cross-bows for projecting the boomarang, and with satisfactory results. Stiffness is essential in the missile,whatever substance it may be made of.

July 14, 1838.

JOHN NORTON.

BARREL CARRIAGES.

Sir,-If my humble approbation to the ingenious suggestion of "Mechanicus" is of any importance, I freely give it. There would doubtlessly be a saving of friction, and also of weight. The machine would, in fact, be a carriage consisting of one broad and hollow wheel, and this would be the whole.

All that friction which in ordinary carriages arises from the weight pressing upon the axle, would be saved. I do not consider the friction of the axle to be much impediment to the motion of carriages, but still it is something which is better to be got rid of if possible. The chief impediments to the motion are the obstacles, asperities, and softness of the ground; the truth of which appears from the comparative small force which is required to move carriages on wheels which step over obstacles (these having been a long time before the public under the appellation of Icapus). But with respect to the barrel carriages, they would require always to be quite fall or quite empty, and loaded with matter of the same specific gravity, otherwise much friction, irregularity, and loss of force would be propagated within, by the material which would tumble about.

*

With respect to the ideas of " C. T. Salisbury," I am sorry to differ from him. According to my view the weight on the axle is not only one-eighth of the load, as he conceives, but is the load itself; yet the friction is diminished according to the ratio its circumference bears to that of the wheel, not on the principle of a lever, but merely because there is less motion and rubbing. The rolling friction must, however, be added to the amount, and this is not so trifling as is generally believed; in proof of which, if a brass wheel of a quarter of an inch in diameter be fitted up with an iron axle of an eighth of an inch in diameter, and an attempt be made to roll the wheel over a smooth piece of box-wood (pressing on the axle), the wheel will not turn, but will slide along; consequently, in this case, the rolling friction is more than half as much as that which the ground would cause if there were no wheels, and rather more than that of the axle itself, because the wheel chooses to slide on the ground instead of undergoing the sliding of the axle, added to the rolling of the periphery. It has, indeed, been an error too general to consider the rolling friction nothing. Another popular error, though perhaps foreign to the subject, is the idea that carriage

See Repository of Arts, March 1815, and June 1821; also Dr. Jamison's Dictionary of Mechanical Science; also the 3rd number of "The Animals' Friend," by Cotes, 139 Cheapside, for the best improvements.