drowned. The vessels were going with the tide at full speed, between 10 and 11 miles an hour. Never gets out of the way of steamers above bridge. The boat will dip from the undulation, but is not afraid of them. Below bridge has almost always been obliged to go out of his course. Has seen a lug-boat pitch her head at the swell, and almost bows under, when she has been in the troughs of the

sea.

Witness some time since left his boat for a few minutes at King's Arms Stairs, Millwal!; on his return he found his boat sunk, and all the gear floating about; found this had been occasioned by the passing of a single steamer. Were the steamers limited to six knots an hour, they would not inconvenience boats at all. When the watermen leave their boats at any of the stairs, they usually hang them off their anchors; and had witness done so in the instance before alluded to, his boat would not have been swamped. (To be coniinued.)

DR. LARDNER'S PROBLEM-THE COMPOSITION OF FORCES.

To S. Y. an Engineer. Sir,-You state (No. 430) that you would be much gratified by seeing a true geometrical solution of Dr. Lardner's problem on the composition of forces, which he has erroneously applied to the solution of a question in current sailing. As the solution is very simple, only requiring a knowledge of the first law of motion, I willingly comply with your request; but before doing so, I beg leave to address a few words to you, which I trust you will receive in good part. Any one would naturally infer from your request that you cannot solve the problem yourself, from which it surely follows, that the person who can do it must, of necessity, know better than you how it ought to be done. Still you would wish to persuade us, that you are competent to direct others in the way it should be done, by the kindly warning you give us that in solving the problem we must bear this and that in mind, &c. Now, Sir, is not this what may be fairly termed the essence of modesty? Again, Sir, in the letter you have addressed in No. 430 to Saxula (poor S. would require to have a thick pate to bear so many hard thumps) you have assumed as high and dictatorial a style as if you really wished to cram the stomach of our senses with a

173

belief, that what you assert must neither be doubted nor questioned. You tell us that Saxula's theory of locomotion is worthless. Be it so; but, Sir, be so good as re-examine and re-consider the contents of your own letter (No. 430), and try if you cannot discover some things which you have laid down as mechanical facts, which, when compared with Saxula's worthless theory of locomotion, will be found to be in the exact ratio of equality. I am, Sir, an unpolished Scotch Highlander, and must speak my mind or die. If I have stated any thing which may not suit the meridian of your more refined notions, you must lay the blame on the rough way I was brought up and educated. And now, my good Sir, we shall proceed to discuss a subject which perhaps you will consider a more delicate repast.

Yours, &c. IVER MACIVer.

Analysis. Let E be the point the boat starts from; F, the point the boatman intends to reach; and ED, the direction of the current. Let M be to N in the given ratio of the rate of sailing to the rate of the current. Join EF; then, in order to keep the boat in the line EF, it is apparent that it must be directed in some line, EH, which lies obliquely against the current. Let EL be equal to M, and draw LK in the direction of the current, or parallel to ED, meeting EF in K, and complete the parallelogram LG. Now, if there were no current, the man, in a certain time, could row from E to L;

and suppose, in the same time, the current to flow from L to K, then if LK is equal to N, then EL will evidently be the direction the boat must be steered, in order to arrive at the point F. For the two forces EL and LK, produce the resultant EK, the diagonal of the parallelogram LG, hence the following

Construction. Make EG=N, and from the centre G and distance M describe an arch cutting EF in K; draw KL parallel to EG, and EL parallel to KG, then will KEL be the required angle the boat must make with the given direction EF.

Trigonometrical Solution. Since M:N :: EL: LK :: sin. LKE: sin. LEK .. sin. LKE N sin. LEK =

M

PRINCIPLES OF SHIPBUILDING. Sir,-In one of the "Notes worth notice," inserted at page 128 of your last Number, headed "Curious Coincidence," the principles of ship-building introduced by Sir Robert Seppings, are strangely enough confounded with those patented by Mr. Redmund, also the ingenious inventor and patentee of the rising hinge. Each of these parties may still continue to wear their respective laurels, for their two systems are as distinct as can well be imagined.

Sir Robert Seppings' invention consists in arranging the exterior timbers of a vessel, so as to form the bow and stern

into an arch; an invention to which I believe his claim is undisputed.

Mr. Redmund's patent was for an entirely new mode of arranging the timbers of a vessel, so as to form a solid arch independent of the exterior planking. In describing and commenting upon his patent, Mr. Redmund observes, "The exterior of those ships which are built with circular sterns (on the plan of Sir Robert Seppings) presents the form of an arch in every direction in which the vessel might receive a shock. But the present system of constructing the hulls of vessels seems to render that form, so indicative of strength, of no comparative utility whatever; as an arch (to resist shocks or violent concussions) should have all its parts firmly connected together, and its abutments made perfectly secure. The present mode of framing the hulls of vessels, leaves a vacancy between the ribs and frames, which said ribs or frames are not firmly connected together, so as to unite their strength until the planking is affixed to them; so that, previous to planking, the hull has no strength whatever.

"Now as this is, I conceive, the foundation of the structure, I respectfully submit that, when in the state ready for planking, the vessel should be, if possible, of sufficient strength to resist all such shocks or concussions as vessels are liable to meet with; so that, when planked, she should acquire the full portion of additional strength which can be imparted to her construction by that process, and that the shocks or concussions, to which all vessels are liable, should not be received on, or affect, the treenails or bolts, which secure the planking to the frame of the vessel.

"Now as the present vessels, previous to planking, are not, by their construction, capable of supporting themselves, and only acquire strength by their planking being secured to the frame or timbers, by wooden treenails or bolts: I presume it is evident, that the greatest portion of every violent strain, shock, or concussion, that the vessel is subject to, must, in a great measure, be received and sustained in some direction or other, by the aforesaid wooden treenails or bolts, which have first given strength to the fabric by securing the frames and planking together. The ribs or timbers not being united close together, there seems to be

During the fine season, which lasts three or four months, the liquid is passed from the fourth house to the boilers, and from thence when it boils to the rope graduating house, where it is repeatedly raised, until the greater part of the salt is deposited upon the ropes, which in very fine weather takes from 12 to 16 hours. In general 27 boilings take 45 days.

The cords are then coated with common salt, so as to be sometimes 0,006 met. (21-3d in.) in diameter; this salt is got off by a cross piece of wood armed with iron plates being raised to the top. of the building, and the cords pulled alternately, so as to strike the salt against the plates. In the bad season the water is slowly evaporated in the boilers, of which there are four all of the same size; they are from between 7 and 8 metres long, 5 and 6 broad, and 0.5 met.^ (19-6 in.) deep.

Yours, &c. Oct. 23, 1831.

H. B. ANDREWS.

Garvey's Plan for Ventilating Coal Mines-Sir, In the description you have published in your 431st nuinber, of the pipeing which I propose for the ventitation of coal mines, it should have been stated, that, by making the pipes return to the boiler, and the in-, sertion of one being a few inches higher than the other, a constant circulation of hot water would be obtained, on the principle of those used for warming, greenhouses, graperies, &c.-Yours, &c., MAURICE (not Michael) GARVEY.

Revolving Houses.-Sir, I called at your office on the day of publication of your 432d No., with an improved plan, which provides against all the objections raised by you, at least as far as human fore sight can. The motion, generally, will not be perceptible. The houses must be locked. An exterior frame also is provided. The inner chambers will not be affected. A revolving house of wood, built firmly, has a better chance of escape than a stone or brick building. Wood is in some measure elastic. The "breadth" of the wind cannot affect the house, the length of the house being opposed only to a space equal to that length. The resistance of the returning stroke can be guarded against by means of springs. A house of wood can be built stronger than is generally supposed; and, if necessary, it would stand a century, revolving, at least, once in an hour at a given rate. Gold and science can cause the blast or hurricane even to pass harmless over the roof,-and a hundred or two would be well laid out in one of the Parks, exemplifying the system.-Yours, &c.. MICHAEL ROUGH, Schoolmaster, 21, Little Earl. street, Seven dials.

Maps of Cities.-Sir, The plans suggested by Lector, in your Number for the 19th of November, for the improvement of maps of cities, has been adopted in France for at least these fifteen years past, to my recollection, but with the addition of having the squares numbered at the top of the maps, and marked by the letters of the alphabet at the side, and with the further improvement, proposed by F. H., of the list of the streets printed at the sides. This double reference in numbers and letters renders the use of the maps extremely convenient; and I have

one of Paris of that description now in my posses- ́ sion. Yours, &c. H., Nov. 30, 1831.

The Tides.-A very remarkable irregularity was observed in the tide of the Hull Dock gates on Sun day week. The moon having entered into her first quarter, gt seven o'clock in the evening of Saturday, it would be high water; by calculation, about noou, on the ensuing day; but the tide rose at the old Dock-gates to 15 feet 3 inches on Sunday noon, and continued to fiow until a quarter past 2 o'clock in the afternoon, ween it reached 16 feet 4 inches, flowing one inch in the last quarter of an hour; and at twenty minutes to 12, it was again high water. there. On Monday afternoon, it was high water at a quarter to two, and on Tuesday morning at halfpast one o'clock. These irregularities in the time of high water arose from the constant north-westerly breezes which prevailed during the previous week.

Zinc Sheathing. The Semaphore, a Marseilles paper, states that the ship owners of that place have found the means of rendering zinc, in every respect, equally applicable to copper for covering the bottoms of vessels. By keeping the sheets of zinc in tallow. or vegetable grease of any kind, in which is infused about one-tenth portion of verdigrease, all kinds of adhesion on the outside, such as weeds, shells, &c., are said to be prevented. This discovery will, according to the estimate of the French journalist produce a saying to the ship-owners of four-fifths in the expense of sheathing new ships.

INTERIM NOTICES.

We have received a letter from Junius Redivivus, in reply to T. M. B., on Temperance Societies, which makes it proper that we should withhold our own remarks upon the subject, till both can appear at the same time.

Another long Parliamentary Report has reached us on Steam Carriages, of which we shall endeavour the to give our readers some account as soon as abridgement in hand of the one on Steam Navigation is completed. We have no doubt of getting through with both long before any practical measure is founded on either.