tally of 3 inches diameter; two of them are joined to the boiler just above the bottom, and the other two just below the surface of the water; the house is divided by glazed partitions into three compartments, for the convenience of forcing one part with out the other; the middle compartment is two lights in width, and the extreme compartments four lights wide; the pipes from the boiler proceed horizontally to the front wall, where they divide, one upper and one lower pipe proceeding to the east compartment, and the other two pipes to the west, and are carried to the ends of the house, where they join to cast-iron cisterns or reservoirs at each end of the house, which reservoirs are 8 ft. 6 in. long, 1 ft. 6 in. wide, and 1 ft. 8 in. deep, having loose iron covers; these reservoirs are filled with water, which communicates by the pipes with the water in the boiler. "When the boiler pipes and reservoirs are filled with water, and a fire lighted under the boiler, the water in heating ascending to the top of the boiler, passes along the upper pipes to the reservoirs, the cold water finding its way back to the bottom of the boiler through the under pipes, and the circulation continues regular as long as there is any heat under the boiler; the hot water flowing through the upper pipes to the reservoir, and as it cools returns back to the boiler through the under pipes. "I have repeatedly after the water has been heated, immersed a thermometer in the reservoirs at the ends of the house, and have only found a difference of three or four degrees between that and the water in the boiler; it is not necessary to make the wa ter boil, consequently if the fire is judiciously managed, no steam will be raised, and no water wasted, but it is necessary to examine the boiler, and add water when any is evaporated. "In Mr. Bacon's two pine pits, a fireplace with a boiler over it, is placed between them; they are each 80 feet long, and 10 feet wide; the western pit is heated by hot water pipes, the eastern one by a common flue, heated by the same fire after it has passed under the boiler. During the severe nights of last winter, thermometers were suspended in these pits and examined every morning; when the pits were uncovered, that heated by the hot water was invariably from 7 to 9 degrees higher than the flued pits. "Brick flues, from the numerous joints and the mortar cracking, are subject to give out at times a sulphurous gas, which is injurious to plants, and even with two fireplaces in a house forty or fifty feet long, it is impossible to keep up an equal temperature in the whole length; the houses get overheated in the neighbourhood of the fireplace, and it is difficult to keep up a proper temperature at the extremities of the flues. "Steam may do very well on a large scale, and when there is constant attention to the fire both day and night; but the objections are the great expense of a steam boiler and the apparatus belonging to it, the frequent repairs that are required, and the necessary attention to the fire, which is as great upor a small as on a larger scale, besides this there is a greater risk of explosion in a hot-house steam boiler, than in that of a steam engine, for steam engines have generally persons properly instructed to manage them, but gardeners or their assistants cannot be so competent. "The heating with hot water has none of the objections I have mentioned of flues and steam; the apparatus is simple, and not liable to get out of order: the boiler has only a loose wooden lid, and no safety valves are required; the quantity of fuel consumed is very moderate, and when once the water is heated very little attention is required, for it retains its heat for many hours after the fire is gone out." Such are the remarks of a practical man, and one who has had much experience with flues and the manage ment of hot-houses and conservatories on the usual plan. He decidedly prefers the plan of heating with hot water, and has petitioned his master to have all the hot-houses and pits put upon that plan, and by which also a very large conservatory adjoining the new house is to be heated. I can bear witness to the correctness of the gardener's description, having seen the thing in operation. The great advantages of this method above others, are economy, simplicity, and facility of management; to what extent it may be possible to carry it with advantage, remains for experience to prove; but the very successful manner in which Mr. Bacon has carried it into effect, makes me think who are in any way concerned in purit an object worthy the attention of all suits of this kind, and will form a sufficient excuse for my trespassing so long on the attention of the meeting; and as some description may probably arise on this subject at future meetings of the Institution, I shall conclude by proposing the following question for consideration, viz. What is the best form of boiler, and proportional size and perpendicular distance of pipes, regard being had to their length, to produce a maximum effect in heating Green-houses, Conservatories, &c. on the above plan? W. CUBITT. Mr. URBAN, THE Poughill, Devon, April 12. HE phenomena of the globe which we inhabit are so interesting in themselves, and so intimately connected with almost every other branch of natural philosophy, that their development has occupied the attention and exercised the inventive ingenuity of the most celebrated philosophers of every age. Most of the ancient as well as the modern cosmogonists endeavoured to investigate the original condition of the constituent parts of the earth, but their duration on an exceedingly confined spot of the great theatre of Nature has been too momentary, and consequently their observations have been too limited to trace with precision the various changes, combinations, and decompositions, which have been effected on the surface of the globe, by the numerous agents that have altered it,-an indubitable proof that the attention of a moment, as it were, is not sufficient to account for operations which have employed the ever-working hand of Nature for ages to produce. Thus finding their resources too circumscribed to explain the grand phenomena around them, the imagination was called upon to supply the requisite desiderata, and from this fertile source they obtained not only an explanation of the different modifications which are continually occurring on the surface, but even the materials that form the nodule at the centre were analysed with apparent exactness, or in the absence of matter, a description of the central cavity was readily supplied. Although the results of these reveries which have been commonly termed theories of the earth, are calculated to give us a better idea of primeval chaos than can easily be formed without them, we must, notwithstanding, acknowledge ourselves indebted to those ingenious writers who have laboured so industriously to form ideas concerning the great phenomena of the earth, for the source of rational amusement, if not of sound philosophy, which they have left us; it is, says an author, an ample compensation for curiosity, even while we want the force of conviction. We feel entertained in perusing their productions, however fanciful their hypotheses, or imaginary their theories; for in their works we find genius contending with impossibilities in the attempt to ac- These are some of the most celebrated and popular writers who have favoured us with theories of the earth. Each author has his disciples and advocates, and therefore since their theories differ so widely from one another, it is not wonderful that there are so many surmises extant respecting the constituent parts and original construction of the earth, especially as they are a subject on which every one is privi leged to enjoy the opinion that he chooses to adopt. Your ingenious correspondent Col. Macdonald has recently published some articles in this Magazine, in which he advances an opinion that the earth is hollow, and he endeavours to establish his notion on the authority of some expressions in the sacred history of Moses. With a reverential regard for the authenticity of the Mosaic relation, and a due deference for the gentleman whom I have just named, it may be asserted that his hypothesis is in direct opposition to the opinion of philosophers of the first order, and to the inferences drawn from very satisfactory experiments. Sir Isaac Newton says (Princip. Prop. 10, Lib. 3), "Since the common matter of our earth on the surface thereof is about twice as heavy as water, and a little lower, in mines, is found three or four or even five times more heavy, it is probable that the quantity of the whole matter of the earth may be five or six times greater than water." May not a conclusion be fairly drawn from this, that Sir Isaac supposed the matter of the earth more dense at the CENTRE than it is at the surface? The same unrivalled philosopher surmised, and experience authenticates the fact, that heavy bodies endeavour to descend towards the CENTRE of the earth. It may be asked, to where do they tend? The answer is, if Col. Macdonald's hypothesis be true, to an empty nothingness: if we admit the truth of Newton's established law, and at the same time suppose the earth a shell, we tacitly acknowledge that we entertain the strange notion that all heavy bodies have an innate propensity to fill the central cavity. The penetrating genius of Newton discovered, and the discovery has been verified by many accurate admeasurements and experiments, that the figure of the earth is that of an oblate spheroid, which is the figure that a homogeneous fluid assumes in revolving on an axis: if we admit, then, the supposition of geologists, that the earth was in a fluid state at the commencement of motion, we must deny that it is at present hollow; for by the laws of gravitation, the heaviest bodies arranged themselves round the centre, and the progressively lighter ones on the surface of the foregoing ones. This is almost Newton's language; he says (vide ubi supra), "however the planets have been formed while they were in fluid masses, all the heavier matter subsided to the centre." The great distance of the centre of the earth from its surface, precludes all possibility of our actually ascertaining its constituent central matter, but we may form reasonable conjectures. The atmosphere which surrounds and revolves with it has been found to be much rarer at a considerable altitude, than it is near the earth's surface, the densest part of it contiguous to the earth is much lighter than water, and water is of less density than the matter composing the surface, and again, the materials of the surface are not so heavy as those which constitute the strata of mines; hence, then, reasoning from analogy, and without assuming too great a license in doing so, are we not justified in concluding that there is a greater probability of the earth's being denser at the centre than it is at the surface? Maclaurin, in his Fluxions, § 868, has submitted Dr. Halley's supposition that the earth is hollow, with a nucleus included, to a mathematical investigation, but from the result, he does not appear to insist on the consequences that would follow from such a constitution of the internal parts of the earth. In the concluding part of the article he says, "When more degrees shall be measured accurately on the meridian, and the increase of gravitation from the equator towards the pole determined by a series of many exact observations, the various hypotheses that may be imagined concerning the internal constitution of the earth, may be examined with more certainty." Since the above-named celebrated mathematician wrote the preceding passage, many admeasurements have been made in different places by Colonel Mudge, the French academicians, &c. but perhaps no admeasurements or experiments which have been effected, have afforded so conclusive an inference with respect to the component matter of the earth, as those made at the mountain Schillellian, under the superintendance of the late Dr. Maskeline. The outlines of the various experimental operations were submitted to Dr. Hutton for calculation, to deduce from them the real mean density of the earth, which the Doctor found to be to that of water as 9.2, and to cient to prove the earth a solid body, it would be an interesting communication, were Col. Macdonald to fur common stone as 9.5, from which very considerable mean density, the Doctor says, it may be presumed that the internal parts contain great quan-nish us with the exact diameter of the tities of metal. Dr. Hutton's conclu- concavity, and the method of detersion (vide his Mathem. and Philos. mining it. The term Dict. art. Attraction of Mountains), ambiguous; according to the idea "hollow" is is so very apposite to my present com- which it gives us, the hollow may be munication, that I shall beg to tran- only a foot in diameter, or the earth scribe his own language, and leave the may be a mere shell; in the latter impartial reader to form his own judg- case, should the venturesome miner penetrate to the inner part of the crust, he may possibly get into the magnum inune, from which he might not easily find his way out again! But an intelligent author observes, that, so far, the deepest penetrations which avarice has made in the globe of the earth, are no proboscis of a knat on the body of an more than the punctures made by the elephant. ment. "We may therefore be allowed (says the Doctor) to admit this law, and to acknowledge that the mean density of the earth is about double of that at the surface; and consequently that the density of the INTERNAL PARTS of the earth is much greater than near the surface. Hence also the whole quantity of matter in the earth will be at least as great again as if it had been all composed of matter of the same density with that at the surface, or will be about 4 or 5 times as great as if it were all composed of water. This conclusion is totally contrary to the hypothesis of some naturalists, who suppose the earth to be only a large hollow shell; supporting itself from the property of an arch, with an immense vacuity in the midst of it. But were that the case, the attractions of mountains, and even smaller irregularities in the earth's surface, would be very great, contrary to experiment, and would affect the measures of the degrees of the meridian much more than we find they do; and the variation of gravity, in different latitudes, in going from the equator to the poles, as found by pendulums, would not be near so regular as experiments have shown it to be." Col. Macdonald has informed us, "that the earth's polar diameter is less than its equatorial by about 27 miles." Taking the earth's diameter 7958 miles, we have 230: 229: :7958: 7929, which gives 29 miles for the excess of the equatorial above the polar diameter. Hence the foregoing ratio, which is Newton's, and obtained by the THEORY OF GRAVITY, makes the difference of the earth's diameter only two miles more than that assigned them by Col. Macdonald. I should like to know the principles from which the Colonel obtained the difference he has given; I have tried the different ratios mentioned by Dr. Horsley in his Mathematics, and have not met with any number that approximates so near in the result to Col. Macdonald's difference as that which I have adopted above. If the preceding facts are not suffi Col. Macdonald has been at some pains to prove that the original meaning of Gen. 2, implies that the earth is hollow; but Moses there describes the earth in its chaotic state; and, therefore, admitting that "David Levy" is correct in rendering the expression "void and empty," I do not see how we can infer from it that the earth was hollow, after "the waters had been gathered together in one place, and the dry land made to appear." Bp. Patrick (see Mant's Bible) expounds the passage to which indigested heap, without any order or I have alluded thus: "A confused shape; having no beast nor trees, nor any thing else with which we now see it adorned." This commonly received opinion. Parkappears hurst, in his Greek Lexicon, informs us, that Pythagoras and Plato seem to have borrowed their TAH (chaotic formed mass, of Moses, Gen. i. 2, matter or atoms) from the nn, or unwhence must also be ultimately deduced Ovid's to be a Non bene junctarum discordia semina rerum.” the 9th verse of the 4th chap. of Ephe- says, "The apostle interprets the Psalmist, and concludes that David, when he foretold Christ's glorification, or ascending up to Heaven, did likewise foresee his humiliation and descent to the earth; q. d. when David speaks of God in the flesh ascending up on high, he doth thereby imply that he should first descend to the earth. Either simply the earth as the lowest part of the visible world, and so opposed to heaven from whence he came down." I do not pretend to know what species of argument can be hence adopted to render the expression, or the commentaries on it, a very rational scriptural proof that the earth is hollow. Perhaps 10 chap. 1 Cor. verse 26, might be quoted, quite as reasonably, to prove that the earth is full or solid, but I refrain from draw ing plausible inferences of this kind from scriptural expressions. I perfectly agree with the ingenious Vicarius Humilis (vide Mag. Aug. 1826), "that these Scriptures were not designed to instruct us in human science, or in any information attainable by our natural powers, but were given us exclusively in those all-important truths will relate to our immortality." The amiable Cowper says, "The critic on the sacred book should be Candid and learned, dispassionate and free, Free from the bias wayward bigots feel, From fancy's influence, and intemperate zeal." At all events, in my opinion, we should undoubtedly be very cautious of advancing an hypothesis, and supporting it on a forced interpretation of a scriptural passage, especially when such an explanation is directly repugnant to the writings of the best biblical commentators, and even to common sense. By doing this, we not only rest our theory on the most slippery basis, but often indiscreetly convert the wisely-intended foundation of our hopes into a pons asinorum, to connect our imaginary suppositions with direct absurdity. Having adverted to Col. Macdonald's paper on the Magnetic Poles (the primary object of which appears to prove that the earth is hollow), I may further observe on the Colonel's assertion, "that Newton, after much study and doubt, at last arrived at the great and important truth, that all space is filled with ether, a subtle spirit or fluid, or air, of vast elastic force: in this the planets move with an exact correspondence between their weight and bulk, and the weight of the ether they constantly displace in their revolutions." This is not very coincident with Newton's own language, Princip. Prop. 22, Lib. 2, where he informs us, "that at 200 miles above the earth the air is more rare than it is at the superficies of the earth, in the ratio of 30 to 0-0000000000003998, or as 75000000000000 to 1 nearly, and hence the planet Jupiter revolving in a medium of the same density with that superior air, would not lose by the resistance of the medium the 1000000th part of his motion in 1000000 years." Again (page 261, vol. 11.), hence also it is evident that the celestial spaces are VOID of resistance, for though the comets are carried in oblique paths, and sometimes contrary to the course of the planets, yet they move every way with the greatest freedom, and preserve their motions for an exceedingly long course of time, even when contrary to the course of the planets." Playfair, in his Outlines, vol. 11. page 198, remarks "that the phenomena of the tails of comets show the celestial spaces to be VOID of resistance." In conclusion, it may be remarked, I have taken for granted, that whenever an opinion is advanced, a consistent objection to it is always allowable, and that the conclusion deduced from experimental evidence or sound reasoning is the only criterion of the probability of fact. Admitting this assumption then, Mr. Urban, Col. Macdonald's supposition, and my reasons for being of a different opinion, are both before the public. We have each submitted our opinion to the same impartial tribunal, the readers of your interesting Publication, who are fully competent to draw an inference for themselves. Yours, &c. JAMES JERWOOD. T. S. K. remarks, that in our Memoir of Dr. Good (p. 276), his last pubcation is omitted; it is in 3 vols. 8vo, entitled "The Book of Nature," the substance of a course of lectures delivered some years back at the Surrey Institution. It is a very useful and interesting work, and fully maintains his high reputation. Dr. Good also composed in 1825 an Essay "On the Origin, Connexion, and Character of the Passions," read at the Royal Society of Literature. (See our vol. xcvi. i. 625). |