A FEW WORDS

ΤΟ MR. MACKINTOSH AND NAUTILUS.

Sir, I stated at the conclusion of my last letter (No. 697), that I had not then made up my mind whether I should answer Mr. Mackintosh's letter (No. 698). In that communication, his method of accounting for the moon always presenting the same face to that of the earth, seemed to me so repugnant to every known law of nature, that I could hardly imagine that he was in earnest. But, from his reply to Nautilus (No. 701), it appears that he was perfectly serious; and, strange to say, he seems to infer from my silence, that I must be a convert to this part of his theory. He states, "I was not ignorant of this when I made the assertion, that the moon does not revolve upon her axis, nor do I see any necessity to withdraw or qualify that assertion from what has been advanced by Nautilus. Kinclaven also objected to the same assertion, but the parallel case of the wheels, and leaden balls, at once enabled him to perceive that it had not been made unadvisedly," &c. Indeed, Mr. Mackintosh, you very much deceive yourself if you imagine, that because I did not reply to this, I have become a convert to that strange part of your electrical theory. Although some such notions as you have promulgated, about the leaden balls and fly-wheel, you may have seen represented in some orreries, surely you cannot be indebted to these artificial toys in attempting to upset what in reality takes place in the laws of nature. I shall make another slight attempt to reclaim you, Mr. Mackintosh, although I am much afraid you are past redemption.

If a body is perfectly spherical and of uniform density, and if it were projected forward, there could be no reason assigned why it should revolve upon one axis more than another; or, indeed, why it should revolve round any axis. But if this is not the case, it is well known (or ought to be known), and can be demonstrated from a combination of mechanical and mathematical principles, that it must revolve round an axis. A stone thrown from the hand always revolves round its axis; a cannon-ball, or bomb-shell, has often such a rapid motion of rotation as to derange its intended line of direction. Now, the earth and moon, and all the other planets belonging to the solar sys

tem, are in figure, oblate spheroids; and it has been demonstrated from facts deduced from physical and mathematical principles, by Sir I. Newton (be it remembered, however, that Mr. Mackintosh holds Newton's demonstrations at a discount of 99 per cent. since he invented his electrical theory !), but more fully by M'Laurin and Boscovich, and by hundreds of others, that bodies of such figures when in motion must revolve round their axes; and the greater the ratio of the equatorial diameter has to the revolving axis, so much quicker will the body revolve round its axis. Thus, of all the planets belonging to our system, the ratio of the equatorial diameter of Jupiter to its revolving axis is the greatest, being in the ratio of 14 to 13 nearly; and Jupiter revolves round his axis in a shorter time than any other of the planets, the time being only 9 hours and 56 minutes.

Mr. Mackintosh has sometimes put other puzzling questions to me. He wishes me to give a demonstration of what produced the first impulse, &c. I must inform Mr. Mackintosh that this proposition is far beyond the "ken" and "scan" of my humble attainments. But if he will propose the question to his own pastor, and if he should happen to be of the orthodox way of thinking, there is no doubt but he will give him a true solution of it.

I shall take this opportunity of making a few remarks on the letter of your astronomical correspondent, Nautilus.—(See No. 697, p. 222.)

Nautilus states, "that he was rather surprised to read the elaborate refutation which Kinclaven, at p. 148, thought it necessary to give of O. N.'s most absurd conclusion, about the latitude of London and the pole star, &c."

Upon turning to p. 148, I find that my whole letter, which contains this elaborate refutation, only takes up three-fourths of a single page; and the portion of it which I take in refuting O. N.'s article, takes up no less a space than eighteen lines! But Nautilus himself (notwithstanding my elaborate refutation) has given another refutation of the same article, still more elaborate, for he takes up no less than nineteeen lines. I am almost wicked enough to suppose, that Nautilus had made the above remark after trying the experiment with the bottle of crusted port,

but that before proceeding, he found it would be necessary to discuss the contents of the bottle. Again, adds Nautilus, "Kinclaven himself may be caught napping now and then; for instance, what does he mean by talking of the pole star's distance from the tropic of Cancer, &c. There is, certainly, an error here.; "the tropic of," I should imagine, is a press error. But if Nautilus will again read over the elaborate article, he will find that in making use of these terms, I was only quoting O. N.'s statement, which he in his turn copied from Leadbetter's Astronomy. Well, Nautilus, to please you, I agree with you it is rather an improper expression-it ought to have been "the difference of longitude between the pole star, and the first scruple of Cancer.'

Sir, In the year 1810, having witnessed the explosion of a powder magazine near Naples, and examined the effects upon surrounding objects, I bethought me of constructing one upon a principle that would obviate, or confine, as much as possible, the danger consequent to ignition. I communicated my plan to General Colletta, then Inspector General of Artillery, who so highly approved of it, as to order one on a small scale, to be constructed under my inspection. A circular pit was sunk twenty-five feet deep, and forty in diameter. The bottom and sides, after being lined with stiff clay, were built up with the best Puzzolana mortar and stone (or brick), and then coated with waterproof cement. The size of the cylindrical chamber, when finished, was twenty feet deep, and as many in diameter. Being protected from the rain, and allowed sufficient time to dry, a wood fire was kept up at the bottom, for several days, till the coating at last was perfectly dry to a considerable depth. A mixture of oil and lime was then plentifully applied, so as to fill up every little crack, and saturate the plaister and wall.

The superstructure for the door and roof above the surface of the ground, was nade as slight as possible, as was also the roof. The object I had in view in this con

struction was, to confine the effects of an explosion to a vertical rise in the air; much more so, even, than in the springing of a mine; and, moreover, a part of my plan is, to give the pit, if the locality require it, an inclination from the perpendicular, of several degrees, so as to direct the possible explosion towards the point where the least damage would accrue. There are many ways of rendering such a magazine perfectly dry and water-tight, all too obvious for me to describe. As a means of abstracting from the confined air, a great portion of the water held in solution, I constructed several copper cylinders, drilled full of holes, which, being filled with lumps of fresh and well calcined lime, and suspended from several points of the roof at various altitudes, absorbed the moisture, if any existed. However well made, gunpowder is not near so deliquescent as is generally supposed; it only becomes so when made with impure nitre, and too large a portion of charcoal.

A magazine of only the above dimensions will contain conveniently, above one thousand barrels of gunpowder; and any number of such constructions may be clustered into one common enclosure in any eligible situation. I am decidedly in favour of lightning conductors, for the preservation of every kind of buildings and ships from the injurious effects of electric discharges. I have seen abundant instances of their saving qualities. But the most secure way of applying them in such a case as the present, is to have them isolated near, but not upon, the magazines. For such conductors to be of sure avail, they must be of a competent diameter, a mass of metal: those generally used are not a quarter big enough. The smallest part should be an inch diameter; and be it borne in mind, that a tube has twice the conducting power of a solid bar. Copper or zinc is far better than iron, in as much as they are less liable to oxydation. The upper extremities should be strongly gilt, or rather plated with gold or platinum. I say "extremities," because it is very advantageous for it to terminate in several branching points. If to preserve a metallic conductor from rust, it be coated with paint, or pitch, or tar, its saving qualities are not merely impaired, but it invites the danger it was meant to parry. The electric discharge

is drawn to the gilded or copper extremity; but, instead of being conducted down the bar, it flies off at tangents before reaching the ground. It is only the surfaces of bodies that can accumulate, restrain, or conduct an adventitious mass of electric fluid. The state of the surface of a conductor, therefore, is of great importance, and consequently the advantage of a tube.

The base of each conductor should be inserted in the ground, at least ten feet, unless water be found at a less depth. The height should be at least forty feet. A scaffold pole is a good support to it; and the latter should be furnished with bracket steps, in order that the rod may be now and then scrubbed with a piece of sand

stone.

The far greater number of accidents occurring from the explosion of masses of gunpowder, have been traced to the defective construction of the barrels, which has caused the powder to be scattered about, and so exposed to numerous contingencies, especially of collision. The remedy to this evil is in the hands of every cooper. Moreover, powder barrels should be well pitched or coal-tarred inside and out, which would defy the damp, or even the water of a well. So much for the present, on powder magazines.

Lam, Sir,

}

Mr. Gretton states, that having occasion to make a drift in a colliery, he was obliged to have the iron tramroad taken up, in order to avoid the local attraction which otherwise would have been exerted on the needle of the compass employed in that operation. This inconvenience induced him to try if he could not find some other guide in forming a straight drift, either level or inclined; and the result was the invention of the instrument sent by him to the society.

The miners' mirror consists of a cast iron circular plate 54 inches diameter, and of an inch thick; on one side of which, and in the middle of the plate, is a semi-globular projection, the diameter of which is 1 inches. On the other side of the plate, and concentric with it, rises a projection which is one inch

from the edge of the plate, in the form of a hoop, one inch high, aquarter of an inch thick at the base, and a little more than one-sixteenth of an inch thick at the edge (this leaves the sides of the hoop sufficiently sloping to allow of its being taken out of the sand with facility when moulded at the iron-founder's). In the inside of this hoop, which is three inches diameter, a mirror is fixed by placing a small quantity of glazier's putty all round the hoop, in the angle at the bottom, and pressing down the mirror firmly upon it. The mirror is then to be attached to one end of a piece of board, about 14 inches long, 5 inches broad, and 14 inches thick, by means of four screws passing through four holes drilled through the plate, within half an inch of its edge, and at equal distances from each other. The semi-globular projection at the back of the plate keeping it at a small distance from the board, allows of the adjustment of the mirror by means of the screws. A tin cover may be fitted on the hoop for the protection of the mirror; but the projection of the hoop only will generally be found a sufficient protection against accidents. This instrument may be manufactured for about 1s. 6d.

This mirror is intended to guide the workman when he is driving levels, headings, or drifts, in coal seams; or levels or drifts in any other strata, when the drifts are required to be driven in a straight line, and in a particular direction, as horizontal or inclining, and, at the same time, towards a particular point of the compass.

Suppose it to be required to drive a heading in the coal, from one coal-pit to another, at a considerable distance; first, let five or six yards be driven in the required direction, as near as may be, without the mirror, then place a dial (miners' compass) at the extremity driven, with its sights in the direction of the two pits (before ascertained on the surface of the ground); then insert the board of the mirror into the solid coal on the side of the drift, near the bottom of the pit; and wedge it fast, in such a situation as that the mirror may be in the line of the sights of the dial; then adjust the mirror, by means of the screws, so as to reflect the light of a candle in the line of the sights of the dial. Then the driving of the heading may be proceeded with, and the workman may, at any time, know if he has proceeded in the right direction, by merely holding the candle by which he works between his eye and the mirror; and if he can see its reflected image in the mirror, of course he has proceeded right; if not, he must know he has proceeded wrong. When the workman gets a considerable distance from the mirror, say fifty or sixty yards, it should be removed nearer to him,

and fixed as before, as the image of the candle is not so distinctly observed at that distance. In this manner, drifts may be driven to any length in the required direction, by ordinary workmen.

The mirror may be made to reflect the image of the candle accurately horizontally, by adjusting the mirror to reflect the image of the candle so as to correspond with the sight of a spirit level: thus it may be useful in driving dry levels under ground; for, in this case, the reflected image of the candle should always be at the same height above the floor of the level as the mirror is.

The mirror may also be adjusted so as to reflect the image of the candle to any angle of elevation required, by making it reflect the light, so as to correspond with the sight of a spirit level, having a graduated arc, and fixed to the proper degree of elevation; thus, the mirror may be useful in the driving of inclining drifts.

The miners' mirror recommends itself, on account of its simplicity, and the ease and accuracy with which the miner may, at any moment, examine his work.

MISCELLANEOUS NOTICES--CHURCH BELLS,

COSMOLITES, ACOUSTICS, ETC.

Sir,-In No. 702 of your miscellany, Mr. W. Baddeley informs me that the idea of bringing the clapper or hammer to church bells, instead of swinging the huge bells roundabout to the clappers, is not new. I am glad to hear it, and only wonder that there ever could have been

any other. I am sorry, however, that he does not inform us where we may see any such arrangement in actual practice.

In No. 696, "A Constant Reader" inquires where the numerous aeorilites, or cosmolithes, are to be found, which I speak of in No. 689, as having fallen in Kent. I should have made an earlier reply to this inquiry, had 1 been sooner able to find the note-book in which I have it recorded. It is in the parish of Lymenge, near Sandgate and Hythe, near the parsonage-house of the Rev. Mr. Price. I have not been on the spot myself, but have seen a parcel of the cosmolites, about the size of an egg, picked up there by my friend, Mr. Charles Herring, of the Regent's-park. Their composition is similar to the generality of such formations, that is, iron, with a little nickel and alumine.

VOL. XXVI.

If your correspondent

who, in No. 701, inquires theader"

cause of such a quantity of steam or aqueous vapour settling on the windows of a room in which gas is burnt, will do me the honour to peruse my paper (No. 2) on the Electrical Theory of the Universe, he will find that I suppose such gas to consist of an electric or galvanic globule, inclosed in a vesicule of This water is set free upon the combustion of the gas, and may account for the deposit he describes.

water

All the expedients for warming rooms by the admission of air, heated either by gas or any other fuel, are noxious. Such heated air should be confined in flues, which, having in the aggregate a large surface, warm the air that is in contact with them. I have seen a room heated by a powerful stove, which dried the' air so much as to make it necessary to place a vessel of water, the evaporation of which restored the necessary humidity.

I have been much gratified by the perusal of Mr. T. Pine's paper, “On the Progress of Vegetation under the Influence of Vapours," in No. 701. If he also will do me the honour to look at my paper above mentioned, he will see that the phenomena he describes, of the speedy absorption of the electricity contained in vapour by the leaves and points of plants, and the consequent deposition on their surface of the water which contained that electricity or caloric, tallies entirely with my idea of the formation of such vapour, and the identity of the caloric, electric, galvanic, magnetic fluids, the light of the sun, and all other known

matter.

The acoustic chair, and the observations of Mr. Curtis on the transmission of sound, in No. 701, are very interesting. Perhaps most people are not aware of the veay extraordinary increase of the power of hearing that may be obtained, by merely placing the hands behind each ear, and pressing them forward so as greatly to increase the collecting surface. Upon this principle, in 1813, I constructed a pair of pasteboard ears for my friend, Monsignor Aquaviva, at Naples; who, being a bishop, but passionately fond

BB

music, and somewhat hard of hearing, was enabled to attend the opera, and hear better than any body else, without exhi

of biting himself in the front of the boxes.*

Yours, &c.

F. MACERONE.

The

27. First. Unduly heated metal may result from a deficiency of water within a boiler. This seems to be a frequent and generally acknowledged source of explosion. foreing-pump, by which a boiler is supplied with water, if at first well regulated, so as to furnish an adequate supply, and if kept constantly in action by the machinery, is subsequently liable to derangement of various kinds. The valves may be put out of order, the passages to or from the pump may be choked by sedimentary or saline matter. The pump may in some cases be heated so as to inject steam and not water. Any accident of this sort will cut off the due supply of water, and the level of that within the boiler will be lowered more or less rapidly. This will be true of self-acting, as well as of ordinary, means of supplying boilers. No one, we believe, has yet been applied, the working of which can, at all times, be relied on. There are, besides, cases in which the forcing-pump is not in action, when the production and use, or waste, of steam is going forward. In some stationary engines, the feeding of the boiler only goes on at intervals, and the due supply is therefore dependant on the attention of the fireman. The same is true of steam-boat boilers when the boat stops at a landing, and indeed the mischief is frequently increased by opening the safety-valve by hand, and allowing the steam, and of course the water, to waste freely. By an approximate calculation† it

If Col. Macerone will refer to our No. 680, he will find this same principle is now being carried very successfully into practice by Mr. Webster.

In the case of a cylindrical boiler with an interior furnace and fine, calling the length of firesurface, d the diameter of the furnace, and the ratio of the circumference of a circle to its diameter, id the extent of fire surface. Then since in a boiler of this kind 1 sq. foot (144 square inches) of fire-surface can convert into steam ⚫356 cubic inches of water, per second; id

the number of cubic inches of water vaporised per second. Again, if we denote by a, the depression in the water level in one second, e the breadth of the water-line, and assume the length of the boiler to be equal to that of the interior cylinder, cl will be an approximate value for the quantity of water vaporised. Equating the two values found, and cancelling 1, we have d x 14 = xc. The depth of water may be assumed at two-thirds the

+356

may be seen that to lower the water one inch in a cylindrical boiler with an interior furnace, or in a boiler of the same form where the fire is applied directly to the exterior, and with an interior flue, will require but from five to nine minutes. If by this depression an interior flue of eighteen inches should be laid bare for an inch in depth, between 102 and 103 square inches of surface would be subjected to the action of the fire, for every foot in length of the flue, supposed level.

28. It thus appears that by accident, or in the ordinary management of the steamengine, a deficiency of water may occur, and highly heated metal be produced within a boiler. Recorded instances show that such has frequently been the case.‡

29. The metal, then, being softened by heat, may give way to the ordinary working pressure of the steam. This will, of course, depend upon the amount of this pressure, and upon the temperature which the metal has reached. The frequent rupture of boilers near the usual water-line, and in a horizontal plane containing very various thicknesses of metal, would lead us to suspect that this is connected with undue heating, which, if all circumstances were equal in the parts of a boiler, would take effect equally, at equal distances from the water-line. But the Committee have not before them any well-established instance in which a boiler without interior flues has exploded merely by the ordinary pressure of the steam, when the diameter of the exterior cylinder, which, calling D that diameter, givés c98 D, and d X 356= 98 x D. The ratio of d to D in a number of cases in practice varies from 4 to 6 and even *7; taking the lower limit or d=4 D, we have 4 DX 14498 x D. Whence 003 inches per second. Or to lower the level one inch would require 5 mins. 16 secs., supposing the water not to each the interior flue.

356

144

For a cylinder with an interior flue, but where the fire is applied, externally, supposing the effees tive fire-surface to be half that of the boiler, the depression per second, will not be less than twothousandths of an inch.

As instances, may be taken, the boiler of the steam boat Huntress, N. VII. Replies, &c. of the Western Engineer, No. 11, Replies, &c. Legislator, Eagle, and Massachusetts, No. XVII. Replies, &c. Explosions at Pittsburg, No. XII. Replies, &c. and Jour. Frank. Inst. vol. iii. p. 70.