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which it greatly surpasses in strength. The success of the manufacture,although simple, depends entirely upon the intelligent observation of the work-men who have charge of it, and who should be willing, conscientious, and welltrained by previous practice.

Wire of the size used in cables, is in the proportion of about one-half strongerthan good bar iron of one inch square. Bar iron of a larger size, if not manu-factured under the hammer, and of a selected material, is still weaker. Goodwire of one-eighth inch thick, should bear at the rate of 90,000 pounds, andupwards, per superficial inch. Those who have experimented on the strength ofbar iron, and have witnessed the rupture of large pieces of wrought or rolled iron,are aware of its comparative want of strengthen such dimensions. It is, indeed,difficult to estimate the strength of large’wrought iron shafts; to insure them,the greatest abundance of material has to be applied. The strength of iron willbe found in proportion to its specific weight, and this in proportion to its density.The latter qualities are imparted to the fibres principally by mechanical action,either by compression or impact. In proportion as the size of iron is reducedunder this process, will the tenacity of the fibres be increased. The process ofwire-drawing appears to be peculiarly well adapted to consolidate the fibres andimprove their tenacity. The finer the wire the stronger it is, but at the sametime, the more expensive. But there is a certain size which yields the greateststrength at the least expense, and this is selected- for bridge building. Theaverage strength of good puddled iron, one inch square, may be rated at 50,000lbs.; good hammered charcoal-iron, of the same size, will bear 60,000 lbs. andu pwards. The strength of bar-iron varies very much, and greatly depends uponthe quality of the bloom, or pig, from which it is manufactured. Another val-uable quality of wire, which should be mentioned-here, is the superior degreeof elasticity it possesses over bar iron, and which is the result of the forciblecompression of its surface during the process of drawing.

The English engineers have to this day refused the application of wirecables, in place of chains, for suspension bridges. The winters in Great Brit-ain are less severe than on the continent of Europe , and in this country; thereis, therefore, in that country less danger to be apprehended from the effects ofintense cold than there is here. The reduced strength and sudden rupture ofbar iron, in cold weather, cannot have escaped the notice of those who are inthe habit of paying attention to such matters. Now it is well ascertained thatthe strength of wire is not affected, in an appreciable degree,, by any changes oftemperature which may take place in the atmosphere. The great safety anddependence on wire, in this respect, should alone be a sufficient reason to give itthe preference over bar iron in the construction of suspension bridges. Thefact, that wire cables are much safer than chains, appears to have been entirelyoverlooked in Great Britain .

The solid anchor chains, which I have employed on the Pittsburgh aqueduct,and on the Monongahela bridge, have been manufactured of a superior material,and with great care. On the Cincinnati bridge, however, I propose to continuethe wire cables below ground for some distance, before they connect with theanchor chains, so that the latter may be altogether out of the reach of frost, andnot exposed to any changes of temperature.

A cable is composed of a great number of strands. Admitting that a fewunsound wires should, in spite of all care and vigilance, find their way into it,their number will be too small to affect the strength of the whole materially.We therefore obtain a combination of strength, which can be depended on for itsuniform disposition. To guard the wire against oxidation, each single strand iscoated with a durable varnish before it goes into the cable, and the latter is4