three quarters of the available strength of | the materials was possibly altogether thrown away. The safety of the whole was made to depend upon its weakest parts; and when decay commenced through process of time or the action of the elements, every successive stage in its advance made the progress more rapid, since the wear and friction increased in double proportion as the fastenings became weak and loose. Sir Robert Seppings at length succeeded in vindicating the claim of the ship-builder to be ranked among the members of scientific professions. By the introduction of the "diagonal truss," the innumerable parallelograms formed by the hull and frame timbers were converted into triangles; and the limits of the magnitude, the strength, and the durability of the wooden walls of England were thus largely extended. The faults of "hogging" and "sagging," which had formerly revealed the weakness of the fabric, often at the first moment of its launch, were almost annihilated; and the huge machines no longer bent under the strain of their masts or the weight of their batteries. But Seppings, after all he had done or projected, could have formed no conception of the vast advance which was erelong to be effected in his favorite art by the introduction of a new material. No possible combination of science and skill could enable him to give to his timber-built ships the magnificent proportions of the Great Britain, together with strength sufficient to encounter the billows of the Atlantic. Still less could he have conceived it possible that such a vessel might be consigned, through a series of mistakes and mischances, to the inhospitable keeping of a storm-vexed Irish beach throughout an entire winter, and yet afterwards be dragged from its shingly bed, and towed into port with only a net result of very reparable damage. Among the properties of matter are some that we may term subsidiary or incidental: qualities which we may be said to discover rather than to comprehend; and whose agencies are of a secret, and as it were stealthy character, so that we cannot always predict their recurrence or calculate their force. Fluid and gaseous bodies present many instances of these perplexing phenomena. While investigating the conditions under which solid substances enter into solution; the rise of liquids through capillary cavities; the motions of camphor and other bodies when placed on the still surface of water; the phenomena of crystallization; the condensation of gases in charcoal; or the inflam mation of hydrogen when in contact with minutely divided platinum-in these and similar cases, we encounter on every side a series of anomalies which as yet baffle all our efforts to group the incoherent facts into a consistent theory. For the present, therefore, we must content ourselves with the functions of empirics and registrars. We must observe and collect the facts which may hereafter furnish a clue to the labyrinth; confident that when that clue is once seized, every step will not only bring us to some result of practical utility, but will reveal yet another example of the divine symmetry of Nature. Upon this point, Paley has allowed himself to be betrayed, by his course of argument, in his "Natural Theology," into a singularly false assumption. In his day the four ancient elements, earth, air, fire, and water, still "in quaternion ran," although philosophers had already seen that it was high time that this category should be reformed. Notwithstanding which, like so many other benevolent writers, he was anxious to console men for their ignorance; and consequently he declared that of these elements, as it was not intended so it was not necessary, and might not be useful, for us to know anything further. Referring then to one of them, water, whose decomposition and constituent elements were at that moment making some noise in the world, he says: "When we come to the elements, we take leave of our mechanics; because we come to those things of the organization of which, if they be organized, we are confessedly ignorant. This ignorance is implied by their name. To say the truth, our investigations are stopped long before we arrive at this point. But then it is for our comfort to find that a knowledge of the constitution of the elements is not necessary. For instance, as Addison has well observed, We know water sufficiently, when we know how to boil, how to freeze, how to evaporate, how to make it fresh, how to make it run or spout out in any quantity or direction we please, without knowing what water is.' The observation has even more propriety in it now, than at the time it was made; for the constitution and the constituent parts of water appear to have been in some measure lately discovered; yet it does not, I think, appear that we can make any better or greater use of water since the discovery, than we did before." Or, in other words, that the discovery of the chemical constitution of the fluid would not prove useful, because it had not been immediately followed by any me use. chanical application of extended and striking It should not have required the splendid contradiction which time has given to this assertion, to have satisfied such a man as Paley how unphilosophical was his deduction, even from his own assumed premises. The various questions which suggest themselves relative to these properties of fluid and solid bodies, are finally resolvable into a single inquiry, touching the absolute nature and condition of a constituent atom. Hitherto the ultimate atoms of bodies have eluded all our attempts at identification. Our most powerful microscopes have failed to render them perceptible; nor are we able, by any process or contrivance, so to separate an individual from the mass as to be entitled to pronounce positively that it possesses any definite form, weight, color, or magnitude; or indeed any single quality, either chemical or mechanical. Not one of its properties can we discover directly. A few we have inferred; but even of our inferences we assume neither their certainty nor their correctness. Hypothetically we speak of the atom as a minute sphere; perfectly indivisible, and consequently unchangeable in form, and incompressible in substance; because the deductions from a multitude of observed facts render the supposition of these properties a matter of necessity. We must moreover conclude that in no known substance are the contiguous atoms in absolute contact; because we have never yet ascertained the limit of condensation from decreased temperature or mechanical pres sure. the atoms cannot have been brought within the circle of the exterior atmosphere of repulsion. Under the influence of an increasing temperature, the two external strata of repulsion and attraction appear to become modified and diminished until, when a certain point of heat is reached, they both suddenly and simultaneously disappear. The body then loses its solidity, the attraction of cohesion having become extinct, and sinks down into a fluid; while at the same time the atoms are not separated beyond the distance at which that attraction would be developed when the temperature is again reduced; and the fluid will, therefore, upon cooling, again become a united mass. Such complicated paraphernalia of forces must we assign to the integrant atoms, in order to explain even the simplest of their mechanical actions. When we attempt to follow up our atomic hypothesis into higher conditions, we find ourselves utterly bewildered as we seek to grasp in idea the complication of forces and principles which must affect the atoms upon their expanding into elastic gases, undergoing solution in fluids, or entering into the innumerable combinations and transformations of the chemical affinities. The imperfection of our present struggles to realize the primary conditions of the material atoms is too apparent. A theory must be singularly at variance with the lucidus ordo of Nature, which obliges us to explain each successive variety of mutual action by the introduction of a new force; just as in the old Greek mythology, every natural phenomenon was placed under the guardianship of a separate divinity; or upon Ptolemy's map of the heavens, every motion of the planets required the inscription of another epicycle. To follow out this hypothesis, we must then imagine every atom to be surrounded with no less than three consecutive strata or atmospheres of antagonistic forces, extending nevertheless in the aggregate to a distance altogether inappreciable. The The limits that are set to improvement innermost stratum consists of a force of by difficulties of CONSTRUCTION, or the arrepulsion so enormous in its strength that no rangements of mechanism, require a very two atoms can be forced into actual contact; different species of analysis from that which around this is a stratum of attractive force, has for its object the properties of natural of very finite action; giving their power of substances; and the terminal problems are cohesion to all the visible particles of matter; susceptible, in general, of merely relative and, last of all, is an outside stratum of solutions. Seldom or never may we be able repulsion, which prohibits the parts when to say absolutely, So far can we go, but once separated from again cohering (except no farther. But we are often enabled to under particular conditions) even when forci- decide among the great objects for which bly pressed together. The extreme tenuity machines are intended-econemy, rapidity, of these strata may be inferred from the and safety-how far the necessities of each fact that two surfaces may be brought so can be accommodated, so as to produce the closely together as to render the intervalresult of most advantage. Yet even here imperceptible by any of our senses; and ye tour verdict can seldom be considered as final. as no cohesion takes place, it is evident that The introduction of a new material, or the and such is the accuracy of the workmanship, that the leakage is barely perceptible. Steam, as applied to locomotion by sea and land, is the great wonder-worker of the age. For many years we have been startled by such a succession of apparent miracles; we have so often seen results which surpassed and falsified all the deductions of sober calculation-and so brief an interval has elapsed between the day when certain performances were classed by men of science among impossibilities, and that wherein those same performances had almost ceased to be re suggestion of a new combination of parts, may at once render easy the improvements that have baffled the ingenuity of man for generations. The history of invention is full of such examples. It would be a curious inquiry to trace how many contrivances have been delayed for years from the mere want of knowledge or skill to execute the works; and obliged as it were to lie fallow until the cunning of the workman could sufficiently correspond with the ingenuity of the inventor. When Hadley first constructed the quadrant still known by his name, for a long period it was perfectly useless in the deter-markable from their frequency-that we mination of the longitude, as the indications might be almost excused if we regard could not be depended upon to a greater the cloud-compelling demon with someaccuracy than fifty leagues. But after what of the reverence which the savage Ramsden had invented his dividing engine," pays to his superior, when he worships as the graduation was so vastly improved, that, omnipotent every power whose limits he caneven in the commonest instruments, an error not himself perceive. It is not surprising of five leagues was seldom to be feared. that inventions, designed to improve the The minute measurements of angular distances forms and applications of steam-power, by the micrometer were long subject to should constitute a large percentage of the similar difficulties. The instrument waited, specifications which are enrolled at the Paas it were, for Wollaston's discovery of the tent Office. Even in France we learn, that means to procure platinum wire so fine, that within a period of four years the following 30,000 might be stretched side by side number of patents, connected only with railwithin the breadth of an inch. The limit way construction, had been obtained in which was reached by this discovery was 1843, 19; 1844, 22; 1845, 88; 1846, 131; followed by another pause. Then came a total 260. Of these we are told that not new advance, owing to the beautiful inven- above three or four have been carried out, so tion of an eye-glass composed of double- as to realize advantage to the inventor; and refracting spar, so mounted as to revolve in all of those were of English origin. a plane parallel to the axis of refraction, and give, by the gradual separation of the two rays, a measurement susceptible of almost infinite delicacy. So in the history of the steam-engine. Bolton and Watt had been long partners, and the theory of his great machine was almost perfect, when Mr. Watt still found that his pistons fitted the cylinders so ill, as to occasion considerable loss from leakage. In 1774 Mr. Wilkinson, a large iron-master, introduced a new process of casting and turning cylinders of iron. Watt at once availed himself of them; and in a few months the inaccuracy of the piston "did not anywhere exceed the thickness of a shilling.' The wonderful perfection since attained may be seen in a rotary steam-engine patented within the last few months. The steamchamber presents a sectional plan somewhat resembling five pointed gothic arches set round a circle; the outline being formed by ten segments of circles all referring to different centres. The piston has to traverse round this singularly formed chamber, preserving a steam-tight contact at both edges; The number of English patents is of course considerably greater. But we doubt whether the proportion of successful ones has been at all higher. Ingenious men have never expended their energies upon a subject where the splendor of past, or possible, successes has so effectually dazzled their imagination, and rendered them unable to perceive the great difference between the relative and the absolute limits of possibility. Because science had failed to predetermine the point at which higher performances became impossible, they too often began to consider it superfluous to invoke her aid at all; forgetting that the problems are quite different ones, to decide between the relative merits of two modifications of mechanism, and to define the ultimate capabilities of either. There is no more striking example of this tendency than is exhibited in the controversy between the two great systems of railway traction-the locomotive and the atmospheric. This controversy has already cost the public incredible sums; and has, moreover, been so dextrously managed that even now, if the money-markets were to re turn to a very possible state of plethora, a plausible prospectus and a new patentee would find it no difficult task to organize another company, and to get subscribed fresh hundreds of thousands towards carrying out an experiment which ought never to have required more than a few months' trial and a short length of working line for its final settlement. For the principles according to which the experiment must succeed or fail, had been determined long since; and it is a fact equally sad and strange, that among the very numerous patents relating to the atmospheric railway, there is not one that touches upon the real turning-point of the question. What was called the "longitudinal valve" or opening, through which was established the connection between the piston travelling within the exhausted tube and the train of carriages, formed the pièce de resistance for the inventors; and very many and clever are the contrivances we find specified for improving or dispensing with this valve. And yet the valve itself entered but as a subordinate function into the equation by which success or failure was to be determined. Granting that its construction was theoretically perfect, and all friction and leakage annihilated, the main principle, which depended upon the laws that govern the motions of elastic fluids, was left wholly untouched. The history of science, nevertheless, contained records which should have prevented this mistake. One hundred and sixty years ago, M. Papin, one of the earliest inventors of steam machinery, invented a motive apparatus involving this identical principle, and which, when tried, was found wanting. The machine alluded to was described by the inventor as "an engine for pumping the water out of mines by the power of a moderately distant river." His plan was to erect upon the stream or waterfall a series of forcepumps, by which air was to be condensed into a reservoir. From this reservoir a close tube, some miles in length, was to be carried over hill and valley from the brink of the river. It was supposed that the condensed air would travel along this tube, and could be applied at the mine, through appropriate mechanism, to keep the pumps going. M. Papin is said to have tried his invention upon a large scale in Westphalia; and it is certain that a similar engine was erected in connection with one of our own Welsh mines; and and in both cases with equally ill success. The machines at the useful end could never be got into motion. The condensers on their side worked powerfully, but the blast of air at the distant extremity would hardly blow out a candle; and although it had been calculated that the condensation would be transmitted along the tube in less than a minute, it was found upon trial that the slight_impulses, which arrived at last, had been three hours on the road. As a last attempt, the motion of the air-pumps was reversed, and the effect tried of employing an exhausted tube. But this mode proved as inefficacious as the other; and the experiments were finally abandoned. The mechanical details, both of the atmospheric and the ordinary railway, are sufficiently understood to exonerate us from the necessity of explanation previous to proceeding to indicate the elements involved in a comparison of their advantages. Looking solely at the chief object with the inventors, economy, we start with the recognized fact, that horse power for horse power, a stationary engine can be built and worked cheaper than a locomotive. This margin of gainand it is not a very wide margin-is all that can be claimed to the credit of the atmospheric principle; and against this must be set as an account contrá, whatever loss or disadvantage may be incidental to the employment of the exhausted tube. The economy in the first construction has to be debited with the cost of the valved tube. This is generally estimated at 10,0007. per mile; and is enough to neutralize the advantage on the other side, even with the addition of some incidental saving in the weight of rails, space for engine sheds, &c. In the cost of working, it is evident that the advantages of the atmospheric system will be much restricted through the invariability of the power. The area of the travelling piston and the power of the stationary engines must, of course, be sufficient to accomplish the heaviest tasks they may ever be called upon to perform; and when the loads are light, the expense can be but little diminished. The same unaccommodating maximum rules also with regard to the frequency of the journeys. Five trains a day will cost nearly as much as fifty, and the gross expense will thus continue irreducibly at the highest point, whatever variation there may be in the performance. It is different with the locomotive system. When the trains do not run, the engines laid up out of use cost little or nothing. Again: the patrons of the atmospheric railway had calculated probably, in the first instance, like M. Papin, that since the velo city with which air of the ordinary density rushes into a vacuum is 1332 feet per second, or 15 miles a minute, such may be the ultimate velocity of a piston within the exhausted tube. Very slight consideration of the real nature of the forces in action necessarily suffices to show, that the conditions of the column of fluid are completely changed as soon as it enters the tube, and that the velocity of impulse will gradually decrease as the column lengthens, until, as in Papin's experiment, it becomes almost imperceptible. To obviate this disadvantage, the tube must be shortened; and in the lines of railway laid down on this plan, a maximum length of a mile and a half has been fixed; thus requiring the stationary engines to be not more than three miles apart. But this increases the original, as well as the current cost; while, by a singular perversity, the operation of the same pneumatic principle impedes the motion and diminishes the power of the tractive piston, and also hampers the efficiency of the exhausting pumps. There is, therefore, at both ends a waste of power sufficient to cover all the margin of economy with which we set out. There is yet another disadvantage attending the use of the longitudinal tube. The faster the piston yields before the column of air—that is, the faster it travels-the less is the active pressure it sustains. In the atmospheric railway the piston moves just as fast as the train; and consequently, to obtain an increased velocity, the load must be lightened in a more than corresponding ratio. But in the locomotive engines, the pistons, with a stroke varying perhaps from sixteen to twenty-four inches, act upon driving wheels of six or eight feet diameter, and will, therefore, recede before the impact of the steam, with only one ninth or one sixteenth the velocity of the train. A far larger proportion of the force exerted by the elastic fluid is thus rendered available. Now that the experiment lately carrying on in Devonshire seems finally abandoned, the great "atmospheric railway question" may be regarded as settled. We only instance it, as a fair ex * Our calculations, given above, appear to be fully borne out by the facts disclosed at the recent meeting of the South Devon Railway Company. It then transpired, that although upon the evidence given before Lord Howick's committee in 1845, the anticipated cost of the atmospheric tube has been estimated at 4 or 5000l. per mile, the expense really incurred was 11,138. The working charges also were reckoned as certain to be far below those of the locomotives. By the test of some months' trial, VOL. XVI. NO. III. 22 | ample of the fact already referred to, that it is their relative solution, with which problems, involving difficulties of construction, are chiefly concerned. For of the mechanical possibility of the machine there never was a doubt. With a certain area of exhausted tube, and a certain power working air-pumps not placed too far apart, all the ordinary necessities of locomotion could be fully satisfied. And if we had known no other means of conveying trains at fifty miles an hour, this would have been sufficient. But the question was not only one of mechanical limit-it put in issue the comparative advantages of rival systems. The atmospheric tube must work betterthat is, more cheaply and more usefullythan the locomotive engine, to entitle it to supersede the latter in the public service. On computing the relative limits of power in the locomotive engine, with reference to the three objects of economy, velocity, and safety, we discover that it is not the consideration of cost, nor the practical difficulties of construction, but the necessity of safety alone, which has assigned to our working velocities their present limits. So long as the chances of collision remain at their existing average, we cannot in prudence increase the rapidity; for even if we could construct our dead mechanism of strength sufficient to endure the concussion, the human machine will not bear it uninjured. Already, fatal results have supervened from accidents of that description, occasioned not by the effect of external injury, but simply from some internal disorganization or shock to the system, produced by the sudden stoppage of rapid motion. But supposing that by better arrangements and more careful watching-even without resorting to the extreme measure of hanging a director or two-we could reduce the danger of collision to the condition of a remote contingency, there are dangers and causes of disorder in the engine itself, and arising during the ordinary course of work, which must be taken into account. Report presented during 1846 to the French Minister of Public Works by M. de Boureuille, In a over 35 miles of road, before the system was discarded, the relative cost appeared to be-locomotives, 2s. 6d.; atmospheric, 3s. 14d. per mile. The chairman, however, stated that by means of various improvements and items of economy, the expenses of the tube might be reduced to 3d. per mile below those of the locomotives. But even upon this estimate it would require a traffic of 90 trains per diem, or nearly one every quarter of an hour, running day and night, to pay 4 per cent. upon the additional outlay. |