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I thought every man was acquainted with, that we have not one yard in London at 45°, nor (except a few yards laid within the past month) any inclined block at any other than between 63° and 64°. Indeed, the only inclined blocks ever yet laid down are those on Parkin's patent, taken out Oct. 1839, and Count de Lilse's, about three months after. Α pavement with an angle of 45° would present so much of the side of the fibre, that a horse could not stand on it any more than if the grain were parallel to the road; and every one that has trodden on a wet polished plank can form some idea of that.

The last error, is to suppose that grooving will diminish the wear to any material degree, especially when it is proved that good wood will wear but one third as fast as stone, (about half an inch in seven years.) This, however, can be the case only when a perfectly uniform and smooth surface is maintained; then there is no concussion, and pressure will make the wood harder.

I am, Sir, your subscriber,
T. H. B.

READMAN'S BAROMETER. Sir,-Your remarks upon my communication relative to barometers, inserted in the October Part of the Mechanics' Magazine, although not altogether strictly correct as to dates, were, nevertheless, sufficiently satisfactory as regarded their intended purpose. In the November Part of your Magazine, Mr. Readman, admitting the principle of suspending, or placing the cistern of a barometer on a spring or balance, to be the only point in which our inventions agree, claims the extension of this principle to the weighing the mercury in the cistern, which he considers to be a better test of atmospheric pressure, than that of estimating the length of the column of mercury within the tube.

In the present instance, I am not inclined to admit that any practical advantage can arise from Mr. Readman's substitution of weight for measure; for, unless the tube be so selected or prepared, that its bore shall be accurately cylindrical within the limits of the mercurial range, his method of weighing would be evidently imperfect; and, unless his cistern be constructed upon the principle

which I have recommended for the constant self-adjustment of the surface of the mercury within the cistern to that within the tube, as indicated by the scale and vernier, no results can be obtained that will not require subsequent correction, even although the tube itself be an accurate cylinder.

If your scientific readers admit the truth of these statements, they may, of course, (provided my principle, so far as I have described it, be fully embodied in the barometers constructed by Mr. Readman,) resolve for themselves whether they would rather estimate the differences of atmospheric pressure by weight, as indicated by a steel-yard or other contrivance, or by measure, as shown by a well divided scale and vernier.

Believe me, very faithfully yours,

CHAS. THORNTON COATHUpe. Wraxall, near Bristol, December 5, 1842.

66

THE MAGICIAN" OF THE THAMES. A new iron steamer has been lately launched in the River, 'yclept the Magician, which, if all be true that is reported of her, has not been unfitly named. She has been built by Messrs. Ditchbourne and Mare, and engine-fitted by Messrs. Penn and Son. Her burthen is 360 tons, and her lines beautiful; her engines are of 110 horses' power. The paddle-wheels are on Morgan's feathering plan. A Woolwich correspondent, who supplies us with the preceding particulars, affirms that she goes "upwards of fifteen miles an hour;" and another 'longshoreman states, in confirmation of this surprising speed, that the Magician started from Woolwich an hour after a Government steamer of 320 horses' power, and within another hour overtook and passed her!

MR. BAGGS'S CARBONIC ACID ENGINE.

Sir, I am not aware if it has ever been suggested to Mr. Bagg, the ingenious inventor of the Carbonic Acid Engine, described in No. 1005 of your Magazine, to attempt its introduction on the common road, where I should imagine it would be more likely to be of importance than on a railroad, comparatively speaking, as obviating many of the (apparently) insuperable defects of a common road steam-carriage.

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New Breakwater.-The steamer Monkey recently arrived in this port, having in tow a cylinder of large dimensions, and freighted with heavy iron work, forming the material for a section of a floating breakwater, the invention of Captain Groves, late of the Rifle Brigade, which is to be moored experimentally in the bay. Judging from its appearance, there is nothing complicated or difficult in its construction. The whole is of iron. The cylinder sustains a grating, attached to it by hoops, and firmly braced by stays passing round the cylinder, and very securely bolted into the bottom of the grating. The draught of water will be about 12 feet, and it will be moored broadside to the sea, both to land ward and seaward. Nautical men say that the doubtful part of the experiment is the ability of the moorings to resist the immense strain to which they will be subjected. Although this experiment is made with the sanction and under the auspices of Government, Captain Groves incurs the whole expense of the work, with the exception of the moorings, which were furnished from Sheerness Dockyard.-Dover Telegraph. The following notice of the actual mooring of this breakwater has since appeared in the London Papers. "Dover, Dec. 6. The experimental floating breakwater, constructed by Captain Groves, has been this day moored in Dover-bay, in 7 fathoms water. It is an iron cylinder, painted black, 50 feet long, 8 feet in diameter, and riding about 4 feet out of the water, nearly a-third of a mile from the pier, bearing E.S. E. from the light on the south pier. A spar, 20 feet high, with a red flag and a bell, will be attached to it."

Method of Obtaining Copper and Silver in the most Minute State of Division.-A solution of sulphate of copper is heated to the boiling-point, and precipitated with distilled zink. The precipitated copper is then separated from the adherent zink by diluted sulphuric acid, and dried by exposure to a moderate temperature. From recently precipitated chloride of silver an exceedingly fine silver-dust may also be obtained by boiling it with water acidulated with sulphuric acid and zink.-Boettger's Beitrage.

Microscope Extraordinary.-A new microscope, of astonishing magnifying power, has just been added to the admirable collection of instruments at

the Polytechnic Institution. Its highest power magnifies an object 74,000,000 times. The wings of the locust, the flea, the house spider, the sting of a bee, &c., fill the whole field of view, being twentyfour feet diameter. The eye of the fly, containing 750 lenses, is distinctly shown, and appeared like a large patterned carpet, and the various animalculæ in water, &c., look like enormous land animals of the most grotesque shapes. The instrument was made by that eminent optician Mr. Carey.

A Railway entirely of Iron.-In consequence of the intended junction of the Liverpool and Manchester with the Leeds and Manchester Railway at Hunt's-bank, a distance of some 200 or 250 yards will have to be executed by the Bolton Railway Company. It will be formed entirely of cast-iron, and will be about eighteen feet above the level of the pavement; to effect which, fifty-one immense cast metal beams will be required, each weighing

about seven tons, and a similar number of pillars, each weighing five tons. Besides this, the entire length and breadth of the road will have a complete cast metal flooring. The estimated weight of the whole is 1030 tons, exclusive of the weight of the wrought-iron and the rails. The railway will be formed in the centre of the street, leaving a carriage road on each side. The design is beautiful; and the work, judging from appearances, will be of the most substantial description.-Mining

Journal.

Prevention of Spontaneous Combustion.-A letter has been received at Lloyd's, from Dr. William Bland, on the subject of spontaneous combustion of wool in ships. The principle of Dr. Bland's system of prevention is the manufacture of carbonic acid gas on board when required, which, by its specific gravity, would subside among the wool, displacing the atmospheric air. He states that 400 lbs. of carbonate of lime, as whitening, chalk, or the poorer marbles, yield about 180 lbs. of this gas, which would fill a space of 20,000 cubic feet, or 500 tons by measurement. The mode of application, he advises, is to place a cask in every hold, perforated two-thirds the height with a hole an inct in diameter, and lined with lead to that height. Into the head of each cask a metallic tube is to be placed, leading from the deck, and protected by a wood casing; each cask to be provided with the necessary quantity of the carbonate, and when required for use, pour down a requisite quantity of sulphuric acid, diluted with four or five times its weight of water, when the carbonic acid gas would disperse to every part of the hold.

Electro-Carbonic Battery.-Some months since, being engaged in experiments with Grove's flatcelled battery, some of the prominent defects of form, construction, and expense, seemed to me to be remediable by another mode of construction, and the use of a cheaper negative element. About the same time, I learned that Berzelius had, in a letter to Dr. Hare, given an account of a battery where coke was at once the negative element and the containing vessel for the nitric acid. I have since made many experiments, and now give the result, which seems most promising. Natural plumbago, or the mixture of it with sand, such as is used in the manufacture of crucibles, gives the form of carbon, which is at once the most effective, cheap, and manageable. A battery was constructed of six cylindrical members of native plumbago, each element one inch in diameter and two inches high, placed in nitric acid of the commercial strength, contained in a cylindrical cup of porous queen's ware, and opposed by a circular zink element amalgamated. The connexion was formed by a wire dipping from each zink into a mercury cup excavated in the top of the plumbago cylinders. This battery of six members gave results which were highly satisfactory. In decomposing power, it accomplishes more than 100 pairs of zink and copper of six inches square each. It gave five cubic inches of the mixed gases of water in less than fifty seconds, or one cubic inch in twelve seconds. It also maintained for nearly an hour, at full incandescence, fourteen inches of No. 30 platina wire, coiled into a spiral. In all other modes of exhibition it shows a proportionate power.-B. SILLIMAN, JUN.: American Journal.

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LONDON: Edited, Printed, and Published by J. C. Robertson, at the Mechanics' Magazine Office,
No. 166, Fleet-street. Sold by W. and A. Galignani, Rue Vivienne, Paris;
Machin and Co., Dublin; and W. C. Campbell and Co., Hamburgh.

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DESCRIPTION OF IRVING'S PATENT CORN DRILL, OR MACHINE FOR SOWING
ALL KINDS OF CORN OR GRAIN.
[Specification Enrolled, December 7, 1842.]

Description.

Fig. 1 of the accompanying engravings is a side elevation of the machine; fig. 2 a plan; and fig. 3 an end elevation.

A A is the frame, to which the various parts of the machine are attached. B is one of the wheels upon which the machine is carried, (the nearest wheel being left out in figure 1 for the sake of clearness.) Upon the axle of the wheels is fixed a toothed wheel C, which takes into, or gears with a smaller toothed wheel, or pinion, D, on the axle of which is fixed another toothed wheel or pinion E. Upon the axle of D there is also fixed two bevelled toothed wheels, F F, which take into, or gear with, two other bevelled toothed wheels, G G, upon each axle of which is also fixed a toothed wheel, or pinion HH, and a circular plate, or disc J J, of metal or other suitable material, called a seed disc. A plan of this seed disc, on an enlarged scale, is given in fig. 3. The toothed wheels, or pinions, H H, take into, or gear with the intermediate toothed wheels, or pinions, K K,which latter take into, or gear with, two other toothed wheels, or pinions, L L, upon each axle of which is fixed another circular plate, or disc, M M, similar to the beforementioned plates or seed discs, which said discs are perforated with holes z z, of any required number and size, as shown in fig. 3.

N is a box or trough to contain the seed; the bottom has holes perforated in it, and there are spouts, or tubes I I, (made of leather, tin, or other material,) attached to each hole, the number and width apart being regulated by the number of furrows, and the width between each furrow. O O, are plates of metal or other material fixed upon the interior of the bottom of the seed box. These plates have recesses in them to receive the circular plates, or discs J J and M M, which are accurately fitted to the recesses in the plates O O, allowing the seed discs to turn freely therein; the upper surface of the seed discs and plates are to be flush. Above each of the holes in the seed box, are fixed small stiff brushes X (sufficiently large to cover the holes in the seed discs,) the surfaces of which brushes press close

upon the upper surfaces of the seed discs, for the purpose of clearing the holes, and only allowing the requisite quantity of seed to pass through each time. To facilitate the passage, and to ensure the proper quantity of seed, the holes in Fig. 3.

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a a are

the seed-discs are made wider on the
under surface. PP are the coulters,
similar in form and material to those
in general use, and arranged to suit
any inequality of surface they may
have to pass over or act upon.
two arms of wood, iron, or other mate-
rial, which are attached to the frame
A A, so as to admit of their being moved
when required, into the position shown
by the dotted lines din fig. 1. Attached
to the arms a a is a rod or axle b, which
passes through the eyes or sockets at the
ends of the coulter blades, and which
eyes or sockets allow the coulters to turn
freely upon the axle or rod b, so as to
act separately or together as required.
Q is a roller or drum attached to the
frame A A, and moving freely upon its
axis. The chains c c are attached at one
end to this roller or drum, the other
ends being attached by a hook to each
of the coulters P P. The ends of the
chains e e are also attached to the
roller or drum Q. These chains are
further attached to the upper ends of
the levers, the other ends of the
levers being attached by a joint to a
board m, which, together with the levers

and chains e e, are used as a press upon the coulters, as will be more fully Attached to the explained hereafter.

roller or drum Q are two other chains, fg, (the latter being indicated by a dotted line in fig. 1,) which pass, one over the other, to another roller or drum R, around which they are passed and attached. The roller or drum R moves freely upon its axis, and has at

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