from the engines to the rudder-propeller, that is an objection which can be of but little force in rivers or canals, where any accident of that sort can always be speedily remedied; while for the navigation of narrow waters, a vessel provided with this rudder-propeller, combines the advantage common to all stern propellers of causing no swell at the sides, with the more peculiar one of being able to run into creeks, wharfs, and other landing places, with a much less offing than any other steamer differently equipped. The Infant Prince is worked by a pair of oscillating engines, manufactured by Messrs. Penn and Son, of 12 horse power, and at the (certainly high) pressure of 35 pounds.

THE CAMBRIAN ENGINE AND BLAXLAND'S PROPELLER.

Sir, The particulars which I forwarded to you, and on which you grounded your notice of the Jane on the river Lea, in the Mechanics' Magazine of the 4th inst., were chiefly taken from the number of the Hertford Reformer, mentioned by your correspondent "S."

The absence of all mention in my particulars of Mr. Crosley, the patentee of the new Cambrian engine," or as the Reformer perhaps very correctly describes him, an eminent engineer"-of the new Cambrian engine itself, and of Mr. Crosley's own account of it-arises, first, from the circumstance that the article of which the said notice forms the postscript is concerning Mr. Blaxland's propeller, and not the new Cambrian engine or of the eminent engineer;'' secondly, from the circumstance "that the applicability of the Cambrian engine to canal and river navigation, from the direct nature of its action, was (not) brought almost as prominently under the notice of the gentlemen present as the merits of the Blaxland propeller itself," for no Cambrian engine was there experimented upon or even exhibited.

As other gentlemen present at the meeting may with equal justice complain to you (by deputy?) that their names have not been transferred from the columns of the Reformer to those of your journal, I here beg leave to subjoin them-Mr. John J. Gripper, Mr. Jasper Gripper, Mr. Y. Crowly, of Hertford, and Mr. Marchant, clerk to the trustees.

I have no desire to impugn the advantages -whatever they may be-of the Cambrian

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engine over that of Boulton and Watt. I know nothing whatever concerning it; but this I must be permitted to say, that Mr. Crosley is the first "eminent engineer" who has proposed to attach a sub-marine propeller to the engine-shaft direct.

You will here see that not one name alone has been "studiously omitted," and where "the small manoeuvre" is to rest, I call upon more than "one of the public" to determine. I am, Sir, yours, &c., C.

WALKER'S WATER ELEVATOR-THE CHALLENGE ANSWERED.

Sir,-What I wished to submit for consideration, was, that the centrifugal pump is exempt from certain disadvantageous drawbacks, from which Mr. Walker's is not altogether exempt; such as,--there being an uniform and continuous motion, both of water and machinery, in the case of the centrifugal pump, instead of a rapid discontinuous or reversing motion-Mr. Walker's pump having also various pieces of machinery beyond what the centrifugal pump requires; and in mentioning these, I did not intend to convey any idea of there being an "outrageous weight" in his machine-inferring merely, that the extra parts must produce some slight friction, and cost and weigh something, at least. As to "T. Y.," he has merely misread my words; I stated that with the same sized pipe more water would be raised; but, naturally, by proportionate power.

Now it was a very natural subject for consideration, whether the above circumstances would not practically effect the relative worth of the machines; but Mr. Walker seems to decline reasoning, on the ground that I have "miscalculated, misrepresented, and know nothing about his invention. It is very easy to assert all this; but I am not aware of any misrepresentation, and should have been glad if he had stated the where and how.

The mode of my calculation was to estimate, according to the laws of inertia, the amount which the water would advance, in each pipe, every stroke, on account of the joint effect of the upward velocity imparted to the water by the maximum velocity of the pipe in its up-stroke, and the receding of the pipe itself during its down stroke, while the water is yet moving upwards, (or, in case of a slower motion of the pipe, before the water has acquired an equal velocity downwards again). It may be that I rather over-estimated the requisite diameter of the main pipes, by not taking into account the effect of their trumpet shape.

The above appears to me to be the most

natural and simple view of its action, but if I am in error, and "know nothing about it," I shall be much obliged, and perhaps it would also be for the benefit of other readers, if Mr. Walker would set me right. If he considers a knowledge of the rationale of its action useless, it would at least be satisfactory to know, for the sake of ready comparison with the centrifugal or any other pump, what weight of water is raised a certain height, by the expenditure of a certain amount of power, measured in pounds raised a given height. If this can be ascertained, it would be more satisfactory than measuring the effect by a man's power, which I suspect may easily vary from 10 to 20 per cent.

According to the best of my understanding, a well-constructed centrifugal pump might raise an amount of water equivalent to 95 per cent. of the whole power employed; but not having had the opportunity of proving this, I should not prematurely condemn Mr. Walker's invention if it does not perform quite so much. I am sorry, that

P.S. I would observe to "T. Y.," who says he does not know how the centrifugal pump referred to acts, that it is, in construction and use, exactly the converse of Messrs. Whitelaw and Stirrat's patent engine, (which obtains power from the descent of water, instead of expending power for raising water); an engine which was praised in the Mechanics' Magazine for its cheapness, lightness, and especially for yielding practically a larger per-centage of mechanical effect, from a fall of water, than any other contrivance in common use.

rge for them to experiment with should be built, and a subscription has accordingly been entered into for the purpose, in shares of 11. eachthe vessel to be the property of the subscribers. The system of Mr. Dempster is ingenious and plausible. We sincerely hope, therefore, that the subscription will be speedily filled up, and that the performances of the experimental vessel may come up to the inventor's anticipations, in which case he will hardly fail to be well rewarded for the time and trouble he appears to have bestowed upon his invention. From the description of it which follows, and which is from the pen of the inventor himself, it will be seen that it divides itself into two parts-the first relating to the build of the vessel the second to the rigging, and that either may be adopted quite independently of the other.ED. M. M.]

1. New Form of Hull.

The advantages of the new form of hull shown in fig. 1, are these: First, The possibility of building a vessel so formed, particularly strong at the bottom. Iron would be the best material for construction, as it would answer the threefold purpose of being strong, weighty, and would leave sufficient capacity for the rerequisite ballast which should be placed low. When the ballast is all fitted for the formation of the vessel's bottom, a deck could be laid over it, and so securely caulked, that, in the event of leaking below, the water would not flow up.

Secondly, A vessel so formed would be less liable to damage herself in the event of striking a rock or any other hard substance, as the shock would be less sudden than that of a vessel with a perpendicular stem, and, unless she was to stick exactly on the point, the chances would be in her favour for again coming off. Getting aground on a sand-bank she would not bump so heavily as a vessel with a long keel, whilst there would be little danger of her breaking her back.

Thirdly, The sailing qualities of such a formed vessel will be good, and her property for quick turning unequalled, as both the rudder and sails can be made at once to act in bringing her round.

Her weatherly qualities, I have no doubt, will be good. It is my opinion that, with a six-knot breeze upon a wind, where the water was smooth, and no current, she would make an equilateral triangular course; that is to say, if she were to sail six miles on one tack, and six miles on the other, she would go six miles to windward.

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My reason for supposing she would be so weatherly are these: When the wind was blowing sufficiently strong, so as to make such a formed vessel careen over, the more she careened, the more length and body of the vessel would be immersed in the fluid to leeward, whilst the contrary would be the case to windward; so that the greater pressure of the fluid on the lee side of the vessel, and acting upon a little weather helm, would, in my opinion, have a tendency to press her to windward of the course she was going; and as the sails of the rig incline remarkably close to the wind, they, of course, will be of assistance in bringing out my hypothesis.

With respect to the stability of such a vessel, I think there can be no question; because the ballast lying low, and the vessel having a good beam, sail may be carried on until every mast went by the board.

The action of the wind, also, upon the weather quarter of such a formed vessel, whilst beating to windward, would have no bad effect; the action of the wind upon a square-sterned vessel retards her progress.

In building a vessel upon this principle, intended to possess the combined advantages of speed, weatherly qualities, stability, and to be capable of performing rapid evolutions, it is required that she must be constructed upon the strictest mathematical calculations; that is to say, the exact dimensions of that portion of her bottom which is intended for the ballast to lie and hold her to wind