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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



LMarch, 



Howed with slight powers of cohesion may thos be rendered enormously 

 tlrong. Indeed we find IhHt fluids, in which the cohesive force is prac- 

 tically at z^ro, cannot be crushed by any pressure we can exert, proviited 

 the hoop or tube that surrounds them can be secured. Now the interior 

 atoms of every substance under pressure are more or less thus hooped-in 

 and strengthened by the exterior. To the strength from cohesion is ailded 

 that from incompressibiiity ; and this elTect is produced in a rapiiily in- 

 creasing ratio as the sectional area of the body is enlarged. A culie of 

 lead suspended from iis upper surface and held together only by coliesion, 

 will break down if larger than 180 feet to a side. If standing upon one 

 side as a base, it might be made of infinite size without danger of fracture 

 from its own weight. 



M'e may conclude, therefor^, that the total force of resistance is amply 

 sufficient to answer any call we are likely to make upon it. It is certain, 

 at all events, that we have not, as yet, built up to the strength of our 

 actual materials. Our marble and granite columns will sustain ten times 

 the weight of any edifice the present generation can wish to erect Or 

 if not, they will use iron. The theoretical limit to the span of our bridges 

 is that only at which the voissours of stone or iron would crumble under 

 the intensity of pressure. The cost and inutility of even approaching to 

 such a limit, will always assign them much narrower dimensions : though 

 large enough, nevertheless, to admit of the accomplishment of that mag- 

 uiliceut project — of which the first design is due to the genius of Telford 

 — for spanning the Thames at Westminster by a siugle arch. Such a 

 work would be worthy alike of the age and the site ; and we see no 

 reason why it should not be undertaken, and completed at least as soon us 

 (supposing promises to be kept in future only as heretofore,) the last stone 

 is laid upon the Victoria Tower. The tubular bridges now in course of 

 erection by Mr. Stephenson, upon the Chester and Holyhead line of rail- 

 way, will probably remain for many years unsurpassed, as specimens of 

 science and engineering skill. 



The hjpothesis that the lorce of cohesion is proportional to the area of 

 section, leads us to the ordinary rule of practice — that as the magnitude 

 is increased, the strength increases as ttie square, and the strain as the 

 cube of the dimensions. The proportions consequently which oiler 

 abundant strength in a model, must be materially ahered when the design 

 is executed at full size. M hen any of the parts are intended for motion 

 a new element is introduced, from the inertia of the moving masses; and 

 thus both the size and the velocity of our machinery aie confined wiihin 

 definite limits. To extend these limits, it is often necessary to solve the 

 most complicated problems of dynamics, and to follow the irain of motion 

 through an intricate series of action and reaction. We must simplify and 

 reduce the number of moving parts, and so adjust the momentum of the 

 inertia, that the resulting strain shall be neutralised, or reduced to a 

 niinimum : and where it is necessary that the direction of motion should be 

 reversed, we must accomplish this object with no such sudden or violent 

 shock as would dislocate the machinery. The difficulty of this attempt 

 iu many instances is proved by the heavy motions and hideous noises tl at 

 accompany the woi king of almost all newly-invented mechanism, and of 

 tiie simplest machines found among nations less skilled than we are in the 

 arts of construction. 



It is equally unscientific, and almost equally dangerous, to give too 

 much stienglh to our constructions as too little. No machine chu be 

 elrunger than its weakest part; and therefore to encumber it with the 

 weight of a superfluous mass, is not only to occasion a costly waste of 

 material, but seriously to diminish the strength of the whole fabric, by the 

 unnecessary strain thus produced upon the parts least able to bear it. 

 This fault is one which is most frequently discoverable in new machinery ; 

 anil which when once adopted in practice, retains its hold « ith the greaest 

 inveteracy. It requires no common powers of calculation, and not a little 

 faith, for men to trust to the safety of structures which have apparently 

 been deprived of half their former strength. 



There can be no belter proof of the difficulties which oppose the adop- 

 tion in practice of any new principle of constiuction or configuration, than 

 that exhibited iu the history of shipbuilding. In no creation of human 

 labour was it more necessary to secure the greatest possible strength from 

 the minimum of material; as none were required to possess such vast 

 bulk in proportion to their mass of resistance, or were exposed to more 

 violent varieties of strain and shock, in the natural course of their service. 

 The men who superintended the public itockyards were often well 

 versed in mathematical science; and were certainly acquainted theoretically 

 with the common axiom, that among right-lined figures, the triangle alone 

 will preserve its form invarinble by the rigidity of the sides, without de- 

 pending upon the stiftnees of the joints. Yet none until a rei ent period, 

 worked out the axiom into its very obvious practical development. For 

 centuries were our ships constructed on principles which caused the whole 

 frame-work to be divided into a succession of parallelograms. Every 

 series of the timbers, as they were built up from the keel to Ihe decks, 

 formed right-angles with their predecessors and w ilh their successors ; so 

 that the whole tabric would have been as pliable as a parallel ruler, but 

 for the adventitious firmness given by the mortices, bolts, and knee pieces. 

 At least three-quarters of the available strength of Ihe materials was 

 possibly allogelter thrown away. The safely of the whole was made to 

 depend upon its weakest parts; and when decay commenced through pro- 

 cess of time or the action of the elements, every successive stage iii its 

 advance made the progress more rapid, since the wear and friction in- 

 creased iu double proportion as the fastenings became weak and luose. 



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 com- 

 prehend ; 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. 



The fluid and gaseous bodies present many instances of these per- 

 plexing phenomena. While investigating the conditions under which solid 

 substances enter into solution ; the rise of liquids through (apillary cavi- 

 ties ; the motions of camphor and other bodies when placed on the still 

 surface of water ; the phenomena of crystallisation : the condensation of 

 gases in charcoal; or the inflammation of hydrogen when in contact with 

 minutely divided platiiiuju — iu ttiese and similar cases, we encounter on 

 every side a series of anomalies which as yet baffle all our efforts to group 

 the iucoherenl facts into a consistent theory. Kor Ihe present, therefore, 

 we 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. 



The limits that are set to improvement by diffioulties of construction, or 

 the arrangement of mechanism, require a very different species of analvsis 

 from that which has for its olject the properties of natural substances : and 

 the terminal problems are susceptible, in general, of merely relative solu- 

 tioiiS. Seldom may we be able to say absolutely — ' So far can we go, but no 

 farther.' But we are often able to decide among the great objects for which 

 machines are intended — economy, rapidity, and safety — how far the necessi 

 ties of each can be accommodated, so as to produce the re»ult of most ad- 

 vantage. Yet even here our verdict can seMoiii be considered as final. 

 The introduction of a new material, or the suggestion of a new combination 

 of parts, may at once render easy the improvements that have bafBi^d the 

 ingenuity of man for generations. The history of invention is full of sucli 

 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 sulBciently correspond with the ingenuity of the inven- 

 tor. When Hadley first constructed the quadrant, still known by his name, 

 for a long period it was perfectly useless in the determination of the longi- 

 tude, as the indications could not be depended upon to a greater accural y 

 than 50 leagues. But after Ramsden had invented his " dividing-engine,', 

 the graduation was so vastly improved, that even in the commonest instru- 

 ments, an error of five leagues was seldom to be feared. The minute 

 measurements of angular distances by the micrometer were long subject to 

 similar difficulties. The instrument waited, as it were, for Wollaston's dis- 

 covery of the means to procure platinum wire so fine that 30,000 might he 

 stretched side by side within the breadth of an inch. The limit which was 

 reached by this discovery was followed by another pause. Then came a new 

 advance, owing to the beautiful invention of an eye-glass composed of 

 double refracting spar, so mounted as to revolve in 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. Boulton 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 con- 

 siderable 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 lew months the inaccuracy of the 

 piston " did not anywhere exceed the thickness of a shilling." The won- 

 derful perfection since attained may be seen in a rotary steam-engine 

 patented within the last few months. The steam-chamber presents a sec- 

 tional plan, somewhat resembling five pointed Gothic arches set round a 

 circle ; the outbne being formed by ten segments of circles, all referring to 

 different centres. The piston has to tiaveise round this singularly formed 

 chaniber, preserving a steam-tight contact at both edges ; and such-is the 

 accuracy of the workmanship, that the leakage is barely perceptible. 



Steam, as applied to locomotion by sea or land, is the great wonder- 

 worker of the age. For many years we have been staitled by sucli a suc- 

 cession of apparent miracles ; we have so often seen results which surpassed 

 and falsified all the deductions of sober calculation, — and so brief an in- 

 terval has elapsed between the day when certain performances were classed 

 by men of science among impossibilities, and that wherein those same pi r- 

 formunces had almost ceased to be remarkable, from their frequency — that 

 we might be almost excused if we regarded the cloud-cumpelling demon 

 with somewhat of the reverence which the savage pays to his superior, 

 when he worships as omnipotent every power whose limits he cannot him- 

 self perceive. It is not surprising that inventions, designed to improve the 

 forms and and applications of steam-power, should constitute a large per 

 centage of the specifications which are enrolled at the Patent Office. Even 

 in France, we learn that within a period of four years, the following number 

 of patents, connected only with railway construction, had been obtained : — 

 In 1843,19; 1844,22; 1845,88; 1846,131; total 260. Of these we 

 are told that not above three or four have been cariied out so as to realise 

 advantage to the inventors, and all of those were of EngllKh origin. 



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 upcn a subject where the 

 splendour of past or possible successes Las so effectually dazzled tliLir 



