Within the downcast-shaft is fixed the feeding-main, which is a pipe leading from the surface to the bottom of the pit, and thence proceeding under and along the pavement to any distance, and in any direction that may be requisite: its progress is here marked by the letters A À A, &c. This pipe (having another inserted) is for the purpose of carrying atmospheric air and gas to the several burners aaa, &c. BBBBB is the evacuating-main for conveying the products of the combustion, which pass along until they reach the upcast-shaft, when they ascend to the mouth of the pit (and higher if necessary), where they are dispersed in the atmosphere. This main is carried along the roof of the pit, as high as it will allow. The supply of air and gas to the burners may easily be regulated by stop-cocks, and the lighting of the lamps may be accomplished, without exposure, by means of one or other of the various modes of producing instantaneous light called Lucifers, Eupyrions, &c., acted upon by a wire passing through an air-tight aperture. Each lamp may be separately extinguished and unscrewed from the mains, so as to be cleansed when necessary, while the others are left burning. For working in narrow excavations, a moveable lamp may be supplied with air from the nearest part of the feedingmain, by means of a flexible tube (similar to that of a beer-engine) furnished with screws and stop-cocks, so as to be lengthened by additional pieces, or shifted to other stations at pleasure. From the required length and flexibility of this air-tube, it might be difficult to insert a gas-pipe, and probably oil only could be burnt. The distance, too, to which the lamp would, in some cases, need to be carried, might render it impracticable to convey the produce of the combustion to the evacuating main; but, nevertheless, it is presumed that the lamp might be made perfectly safe:-in the first place, by having the chimney of sufficient length to prevent the possible egress of the flame; and, secondly, by providing that the heated vapour, before mingling with the atmosphere of the mine, should have to pass through small holes, similar to those in the rose of a watering-pot, and which holes might be lengthened into tubes, or even passed through water if found ne cessary. The inflammable gas of mines, if it enter the Davy-lamp, must be carried along with the current that supplies the flame, and would not readily pass into this insulated lamp, the current of which would always press outwards. The proposer is aware that the preceding is merely a sketch of a general principle, which will require to be modified according to particular circumstances. He acknowledges, too, that, in many cases, its adoption would lead to much expense; but, as a counterpart to this, may be placed the annual saving, from premature destruction, of a great number of valuable human lives. Charlotte-street, Bloomsbury, Feb. 8, 1836. DAVID BOOTH. PREVENTION OF ACCIDENTS IN MINES. Sir, From reading the evidence on accidents in mines, I am induced to lay before you my views on the subject. I think that any modification of the lamp would be useless. Ventilation would un doubtedly answer could it but be perfected; the difficulty being the removal of the inflammable gas, a current of air through every part of the mine seeming to be impracticable. The plan that I should think would answer would be by electricity. The damp and dust might be prevented from coming into contact with the electrifying-machine by enclosing it in an air-tight metallic casement; letting one end of the axis extend through the casement for the purpose of affixing a handle, &c. The orifice must be made air-tight. Part of the conductor must also be extended through the casement. This orifice must have a tube of glass inserted into it for the purpose of insulation, and must likewise be made airtight. A jar must be used; from the outside of which wires must be extended to all parts of the mine, the wires to be supported by posts, &c. By discharging the jar the carburetted hydrogen gas would be decomposed, water would be formed, and carbon deposited in the mine in a state of very fine dust. Should carbonic acid be formed, small pools of limewater would absorb it. The nitrogen that would be set free would be in an isolated state. Iron filings, moistened with water, would cause the nascent hydrogen contained in the water to be evolved which possesses an affinity for the nitrogen; ammonia would be formed; and the entire mine would, in consequence, be occupied by no other air or gas than atmospheric. The electrifying-machine being constantly used, say four or five times in twenty-four hours, and for about five minutes each time, no great quantity of carburetted hydrogen gas would accumulate; the explosions each time being, of course, very feeble, neither loss of life, nor other accidents, could ever occur. I have an electrifying-machine fitted up corresponding with this plan for exhibition, and shall be glad to show it to any gentleman interested in the subject. Yours most obediently, AUGUSTUS BRACKENBURY. 55, George-street, Euston-square, St. Pancras. THE HERAPATHIAN (not "CONTROVERSY," BUT) RETREAT. Sir, It appears from the communication in your last Number from Mr. Cooper (one of those numerous and handy friends of Mr. Herapath, who constantly put one in mind of the proverb, "Whoever advocates his own cause is sure to have a fool for his client"), that it is at length found necessary, in order to uphold Mr. H.'s moral as well as mathematical reputation, to invent falsehoods. "Yes, gross falsehoods!" Well, what next? I shall not suppose that Mr. Herapath himself could have had any hand in countenancing or giving currency to such falsehoods. But as matters have taken this turn, he ought to lose no time in giving an explanation in his own proper person. If he do not, then he must not be surprised, if told some fine morning to "hang a calf's-skin". he knows where. The supposition of Mr. Cooper (" aut Diabolus aut Herapathius"), that Iver McIver, S. Y., H., Miso -Philo-Anti-H., F. Meredith, &c., may be one and the same person, you have yourself, Mr. Editor, flatly contradicted, and better authority on the subject there cannot be. Permit me, however, to make a few remarks. The idea that S. Y. (an engineer, and one of your oldest contributors), should be identical with me and a backer of mine, is truly farcical. Twice in the course of this controversy has S. Y. endeavoured to show (see No. 641 and 647) that the velocities which, I calculated for a descending plane (No. 640), were derived from false principles. If S. Y. wished to back me, it must be confessed that he took a very odd method of doing so. S. Y., however, in his last communication, has candidly admitted, that on this head he was in error, and in a very fair way he has explained how he was misled. Who the "strong-of-hand H." is, or Miso-Philo-Anti-H. may be (although I am free to confess, I suspect, they are identical), I know not; but I refer Mr. Cooper to your own editorial note, p. 563, No. 633, and let him couple that with your note No. 652, p. 381, and if both do not convince him of his erroneous suppositions, then, in plain English, he must suppose that you yourself, Mr. Editor, must have deliberately deviated from the path of truth. With regard to F. Meredith, of Cambridge, I know no more about him than I do of the man in the moon. I wished, sir, for no backers. If Mr. Herapath, or any of his competent mathematical friends can fairly demonstrate (which has not yet been done) the truth of his theorems, then I shall at once acknowledge myself in error. Want of time has hitherto prevented me from giving an analysis of the last production of Mr. Herapath (alias A Looker-on). He states, that where the starting velocity is 25 miles per hour, or 363 feet per second, and the ascent 49 feet per 707 chains-or 8 miles, 14.74 yards-which gives a rise of 1 foot in 952-28, then, according to the dictum of Anti-Carper (another of Mr. Herapath's intimate relations) the velocity per mile per hour up hill will, by Iver M'Iver's theorem, be imaginary. Mr. Herapath, however, does not give the arithmetical result of this imaginary velocity; no doubt from the consideration, that if he had done so, it might have been supposed to be " romancing." But as I am now getting a little acquainted with the Herapathian system of arithmetic, I shall now do it for him. Here, then, it is : (363)2—643 × 2-113!!! 46662 15 952 28 22 Oh, Mr. Herapath! oh, Anti-Carper! and oh, (impartial) Looker-on! I am much afraid that Iver M'Iver will really be an old man before any of you arrive at the years of discretion. 2g S sin. i But what is the real fact? Supposing, as they do, that the engine were not allowed to exert more power on the ascending plane than what was necessary to produce a velocity of 25 miles per hour on the level-why, then, the whole space V2 passed over would be S= (363)2·952.28 641/ and 1,052 yards, that is, instead of the engine and train arriving at the extremity of the summit with a negative velocity of 2-113 miles per hour, it would ab-solutely come to a dead halt before it reached half the distance !!! = 19,901 feet, or 3 miles Again, on the descending plane, Mr. Herapath forces me to apply the same power of steam as was employed on the level and ascending plane; and then he calculates from what he styles my theorem, that the velocity at the bottom (distance 8 miles and 1,474 yards,) will be 45.72 miles per hour. Well, perhaps, this might not be considered a dangerous velocity; but if it were, I must inform Mr. H. that if he would allow me to regulate the steam, I could show how the engine and train might arrive at the bottom of the descending plane, with any velocity, between the limits of 0 and 45.72 miles per hour. Mr. Herapath speaks of calculations made by Dr. Lardner on this subject, given in his evidence against the Great Western Railway. Now, as I happen to know Mr. H. was present during that examination, perhaps he will favour us with the principles of that calculation, as I find it is not given in the evidence of Dr. L., as published in the Mechanics' Magazine. Feb. 8, 1836. I am, Sir, yours, &c. IVER M'IVER. THEORY OF NUTATION. Sir,-Although the attraction of gravity might be sufficient to produce perturbations in the planetary system, or to be the cause of motions in the mass of planets, exclusive of their annual and diurnal motions, still I consider nutation and libration to be the results of other causes; and so far from either of them being an accidental mode in the planetary motions, I think I can show satisfactorily that they are as necessary and absolute attributes of the planet as its orbital or axical motions. It may be deemed presumptuous in me to impugn the efficacy of gravitation to produce the various phenomena in celestial motions; but, I shall be happy if I succeed in drawing your readers' attention to the subject, although it should ter minate in the destruction of my hypothesis. To economise space in your valuable pages, I shall confine myself for the present to the development of the causes of nutation; and I ground them upon propositions so evident that they amount almost to axioms. 1. Heat expands the bulk and volume of matter. 2. The resistance to a body in motion is proportional to the extent of surface opposed to the resisting medium. 3. Whatever cause LESSENS or AUGMENTS the projectile force of a planet, ACCELERATES or RETARDS its circular motion--and the same is true conversely of the attraction of gravity,--whatever cause LESSENS or AUGMENTS the force of gravity, RETARDS or ACCELERATES the circular motion. First. That heat expands the bulk and volume of matter is a proposition familiar to every one. A rod of iron made red hot will not enter a hole it just fitted when cold. Water by heat is generated into steam, which occupies eighteen hundred times the space it did before being heated. A bladder, partially filled with air, on being exposed to the heat of a fire, will have the air within it expanded to the full dimensions of the bladder, which will burst if the heat be long applied. The same facts can be applied to our globe. What is true of its component parts, is true of it as a whole, -that is to say, heat expands the bulk and volume of our planet; and the converse of the proposition is also true. Cold* contracts the bulk and condenses The principal source of heat to the earth is the sun. The vicissitudes of the seasons are produced by the variation of the quantity of this heat, in the earth's annual course round the sun. It follows the volume of our globe. This phrase is incorrect, strictly speaking; cold being held to be an inferior degree of heat. from this circumstance, that opposite hemispheres of the globe are unequally heated, in fact, that one hemisphere is expanded while the other is contracted. From the autumnal to the vernal equinox, the northern hemisphere suffers contraction, being deprived of the direct influence of the sun's rays; and, from the vernal to the autumnal equinox the southern hemisphere is submitted to the same privation. The equalisation of heat on both hemispheres must occur sometime about the equinoxes, and the maximum and minimum degree of heat of each hemisphere about the time of their summer and winter solstices. Second. The centre of gravity of the earth keeping the same position, however unequally the hemispheres of the earth may be expanded, it follows, that if the earth in its orbit he opposed by any resisting medium, an oscillatory or swinging motion will arise, the axis of the earth forming angles with the plane of its orbit, because the hemispheres are unequally expanded; and, hence, the resistance to one hemisphere will be greater than the resistance to the other, proportionally to the difference of the surfaces opposed to it. Suppose, for example, that the greatest degree of expansion were in the southern hemisphere-to that portion of the globe the greatest resistance will be offered; consequently, the northern hemisphere will advance with a velocity greater than that of the other, in proportion as its opposing surface is less than the surface of the other; and a spectator at s, having the stars' vertical, will from nutation describe the arc s' s'', while the star s' will appear to move northward in the arc s's". The same phenomena will ensue to an inhabitant of the southern hemisphere; and when the northern hemisphere has the greatest expansion, the opposite phenomena will take place. The angles s's" and ss", may be taken as consistent quantities, although the times in which they are described, in decrease continually from the causes consequent upon the truth of the third proposition. To illustrate the truth of the second proposition, a piece of wood may be shaped in the form of an egg nearly, and loaded so as to be about the specific gravity of water, or just enough to sink it under the surface of the water. This piece of wood may be contrived to float so, with either end uppermost; and if a string be attached to the centre of gravity, and the wood dragged through the water, it will be found that the smaller end will advance, and the greater recede, or an angle will be formed with the surface of the water and a line which would pass vertically through the wood if at rest. Hitherto, I have been reasoning upon the assumption of a resisting medium, and the truth of the proposition in detail must rest, in a great measure, upon the truth of the following: : Third. When the projectile force and the attraction of gravity acting upon the mass of a planet are equal, the planet will describe a circular orbit, and persevere for ever in it, performing its revolutions in exactly the same period of time. When these forces are unequal, the period of the planet will be either accelerated or retarded, depending upon the excess or defect of their proportions to one another. Now we find from the results of physical investigation and from actual observation, that the periodic times of the moon and of the earth are gradually being accelerated, and the same fact may be true of the other planets of our system, which may be determined affirmatively in course of time, when a greater number of observations shall have accumulated to decide upon. Whence arises this acceleration? The original projectile impulse the planet received must be gradually lessening, either from an increase in the original quantity of gravity or from some opposing force. Observations cannot be made with sufficient nicety to determine whether the first supposition is the true cause of the acceleration: the effects of a resisting medium are, how, ever, more familiar to us, and we ought |