New Contrivances Ancillary To Engineering.*

typed , the contractor and builder take the places of the engineer and architect ; but Ave can no more compare the former with the latter , than we can compare the modern teachers of alphabets with Cadmus , their inventor . The true engineers and architects are those who have the designing power in the new and useful , and the beautiful ; and these men exist now , as ever , when the demand arises for their talents by new conditions of circumstances .

The materials of stationary structure aro natural and artificial —timber and stone , bricks , cements , and metals . Neither timber nor stoiie is in all cases durable . To provide for the former we artificialize it by chemical injections , as creosote , lime , and other substances . The former renders it durable , but combustible ; the latter renders it brittle ; and therefore these contrivances are imperfect . Stone is not often chemically homogeneous , and it is liable to destruction by exposure to a vitiated atmosphere .

TOY this reason it has from very early periods been waxed , painted , varnished , ancl injected ; and , in these modern clays , artificial stone has been produced by chemical contrivances , with the advantage of being moulded into shape without the labour of cutting . Brick or terra cotta—literally eoohed earth—is a more durable material than many kinds of natural stone ; and , as experiment goes on improving and cheapening the processes , it Avill probably be rendered indestructible by the atmosphere ,

whilst chemical cements , combining with mechanical form , will render it homogeneous . Many are the chemical and mechanical contrivances that have already given value to and cheapened bricks ; but for all that , a brick building is still a very imperfect kind of structure . Chemical cements are in truth artificial stone of better or worse quality , used for joints and as a cover for other material Cement , rightly made and cheap enough , is material to form buildings and bridges as one solid rock ; and

this is done by the French under the name of beton . If chemimically impervious to the atmosphere , this Avould he the best class of structure for walls , buildings , and bridges , unless want of space should render it desirable to use the stronger and thinner material , metal .

For moving matter , engines , vessels , carriages , machines , and instruments of peace and war , metal is fast becoming the cheapest most available material . With a given weight in a large vessel , iron will carry a greater load than timber ; yet it is little over thirty years since iron shipbuilding became a practice . What a host of brain-working contrivances have they been ivhich have enabled us to cut masses of iron as Ave do cheese ere the original iron vessels , looking like pots to boil entire whales in ,

culminated in a Warrior ; still only an approximation to what we must ultimately achieve ere tbe world will be satisfied that England is only the veritable policeman of the ocean , permitting no seawaymavi of violence to harbour thereon . We have yet to weld our sea Warriors into one homogeneous mass , dispensing with rivets ancl joints ; we have yet to make the iron hull a surface to which neither corals nor lichens nor barnacles will adhere ; we have yet to liken tne speed to that ol swift fishes or

locomotives on land ; and A \ 'e have at the same time to make such craft Avholesome , pleasant , and safe dwellings for our sea warriors against sea and rock and foeman . But space is denied ns to say more now . Iron Girders for Bridges . —Since the advent of railways , roads

have become more level than of old , arched bridges of stone cease to meet the requirements of the time , ancl flat girders of Avrought iron are rapidly taking their place . There are two principles employed in iron girders—compression and tensile strain , the tensile principle being unknown in stone bridges . In wrought iron the power of tension and compression may be assumed to be nearly equal , if they could be tried under the same conditions . The compressing action has a tendency to flatten

the molecules transversely , the tensile action has a tendency to flatten them longitudinally ; but in tbe two operations a new element comes in , that of " buckling . " With the tensile strain the bar is drawn to a strai ght line ; with the compressive strain the bar is constantly thrust into a curved line , unless it be of large dimensions . For this reason an iron wire , to whicli a heavy load may be safely suspended , will scarcely svpport a fractional part of that load under compression in the same length .

In constructing a straight girder , it is usual to make the total depth from top to bottom one-tenth or twelfth part of the total length . The upper line must have sufficient area to counteract buckling , as Avell as sufficient strength to resist crushing . The lower line is simply a chain or cord of links or plates . The ultimate resistance to breakage must depend on the links or

chain beloAV . It is obvious , therefore , that the most favourable condition for the use of wrought iron is that of tensile strain . In this Exhibition there are many drawings and models of iron suspension and other bridges . We have the design for the Charing Crosss Suspension and the Clifton Suspension . AVe have the triangulated girder , exhibited by Col . Kennedy , the engineer ofthe Bombay and Baroda Railway , as a sample ofthe

rigid girder . We have an enormous box lattice of the Zollverein , and also a similar kind in the Austrian department . In the French department we have a sample of a framework of wrought iron , a top and bottom frame held , together by similar vertical framings , with millions of rivets ; and we have also the peculiarsuspension bridges of Mr . Brunei , in which chains are suspended from tall towers to carry a roadway ; and , in order to dispense with anchoring chains , tbe towers are framed together with

wrought iron tubes , in order to prevent them from pulling over ivith the weight . In the Austrian department is exhibited a rigid suspension bridge , the best construction that has yet appeared for the disposition of the material , by Schnirch and Fillunger . A bridge of this class spanning the Danube at Vienna has now carried two lines of railway since September , 1860 . The span is 27 <_ feet , and the width 36 feet . The weight of material is 4-90 tons

of Avrought iron , and < tl tons of cast iron ; total , 531 tons . On each side the chains are doubled , and formed of links 10 feet in length , in numbers eight and nine to each chain . One chain is-4 i feet above the other in a parallel curve , the links breaking joint . Diagonal bars , serving both for thrust and tension , stretch from the lower bolts to tbe upper , in a triangulated form . Thus two diagonals and a chain link form a triangular truss , and the whole forms a rigid suspension beam , the ends rising at the towers to three times the central height , and thelevel roadway is suspended from the link bolts . It is stated that an ordinary lattice bridge for the same span would have

required 802 tons of metal . It appears , therefore , that while a straight triangulated girder requires a depth equal to a tenth or twelfth part of tbe length ,, to prevent buckling , one-seventieth of tbe length is sufficient for triangulated suspension chains , while the rise or gradient of the chains is only about one hi seventy . Pressure on the model gives satisfactory proof of the stiffness and freedom from oscillation , both vertically and laterally , without the aid of stay

chains or ties . The only disadvantage in the bridge , as compared with straigh . girders , is the necessity for towers and anchoring chains to balance the wei ght of the load , and prevent the towers from pulling over . In juxtaposition with this model is exhibited another model the exact reverse in principle , It is a trinangulated girder in an arch form , composed of similar links and triangles , but all in cast ironacting whollby compression . The links are

practi-, y cally shortened to one-half by stay bolts passing through theirmid length , to prevent them from buckling . An enormous mass of stays and ties and diagonals pervade the structure , which is complicated in all parts . Massive stone abutments equal to half tbe length of the bridge , are required to sustain this thrust both ways . If cast iron bridges are required in an arch form , the best and simplest structure is that spannjng the Thames at Southwark .

In materials for girder making , tbe Butterley Iron Company have been the most successful . They have produced a wrought iron beam , the vertical web of which is 3 feet in depth , and the top and bottom tables each 9 inches wide , the whole well proportioned ; and it is stated that these beams can be produced 60 feet in length . The beam is rolled in three pieces , tbe two tables and a broad middle iveb , and welded up in two seams ; but tbe producing it in one single piece is simply a question of larger rolling machinery . When these beams are produced homogeneously , bridge building will become a very simple

process . Chains , —Years back a Corsican captain of the sea , named Siseo , having experience of the breakage of chain cables made in the ordinary manner , set himself to devise a better plan . It is a known quality in iron and steel , that the smaller the size the more perfect may be the manufacture . Thus , if rolled iron of one inch iu diameter will carry 28 tons , the same Aveig ht of metal in fine steel Avire will carry 120 tons . Sisco Avas not

successful in making and welding thin links with wire , and so he tried the same with iron hoop , the lamina , of which he brassed together , and was successful . His cables , with hoop iron links , sustained a far greater proportional strain than those of solid iron . The Corsican found a capitalist in Madame Siuibaldi to