an experience in the country itself. The forests of Brazil, unlike pine forests, never presented a number of trees of the same description in one spot; and serviceable timber was very limited. It was frequently necessary to make a selection of one tree only in the midst of several hundreds of no value whatever. In fact an Engineer, standing in the magnificent primeval forests of Brazil, might paraphrase the words of the Ancient Mariner, and exclaim

When visiting the Brazilian railways last year, he was sorry to find that native timber was being largely used as sleepers. He saw, for instance, on the San Paulo Railway, large piles of native timber sleepers. These sleepers were made up of many varieties of timber, more or less durable; they were of irregular scantling, and being exposed to the sun and weather, they were splitting freely. He believed that the greater part of those sleepers, after being down for two years, would be found to be decayed; and long before the lapse of two years the spikes would become loosened, on account of the tendency of the timber to split. The result of his experience, in the use of timber in Brazilian soil, made him regard its employment as something like putting "ashes to ashes." He knew of no instance of any attempt to creosote the native timber, which, when worth anything at all, was hard, and had a tendency to split. On the same railway timber telegraph posts were being erected. Now he knew for a fact, that on the Dom Pedro Segundo Railway (Rio de Janeiro) three several sets of timber telegraph posts had been put up; and the Company, after having incurred very great expense and annoyance, were now erecting posts of iron, notwithstanding that their line passed through some of the most magnificent forests on the face of the globe. Considerable experience induced him to draw the general conclusion, that the use of native timber sleepers in all such countries as Brazil, was very unadvisable, first on account of the difficulty in selection, and secondly on account of the trouble and expense in keeping the permanent way in a proper state of repair. In such countries, for years to come, high velocities would not be required; and with moderate speeds iron sleepers were safe and economical, and they might be considered as indestructible.

Mr. F. W. SHEILDS said, four, or five years ago he went to Brazil to lay out works of some magnitude. At that time he inspected the works on the Pernambuco Railway, with the view of applying the experience gained upon that line, to a railway at Bahia, then about to be commenced. The conclusion he came to was, that all works of art in Brazil would be more safely estimated and more satisfactorily carried out, upon the supposition that the materials should be designed and be prepared in

England, in such a manner that they could be put together, with the least trouble and labour, after their arrival in Brazil. He was led to this conclusion, not only on account of the perishable nature of the timber, and the generally inferior quality of the masonry, but also because, in a hot climate, little reliance could be comparatively placed upon the labour of even the English workmen sent out there, as their nervous system was generally debilitated by the effects of the climate. It was therefore far safer, as a general rule, to design works of art, in the simplest form, with English materials and have them erected in the country, no matter in what part it might be. He might add, that in the course of his explorations, he examined some rude bridges which had been erected about three years, and on breaking the surface of the timber, which he could easily do with his foot, he found the interior of the timber filled with white ants. This satisfied him that the use of native timber was generally to be avoided in permanent works. With regard to iron work, it appeared to him, that the use of corrugated iron, so much employed here for roofing, would in a country like Brazil be a great mistake. The native tiles laid upon the rafters, with no ceiling underneath, formed the best kind of roofing for that country, as, although it made a heavy roof, it was not only the best protection against the heat of the sun, but it also afforded the best means of ventilation. In a large railway viaduct, which had been intrusted to him to design, and to arrange for the execution of, cast-iron piles were required to be used, at a considerable depth in sea water. It was for some time a question, whether the salt water and other elements would not have a very deteriorating effect upon the cast iron; but he had recently received a report stating, that immediately upon the iron being put down into the water, it became so thickly encrusted with marine shells, as to form a complete protection against the action of the salt water, so that there was every probability that these cast-iron piles would endure for a long period. In using wrought iron, in situations exposed to the atmosphere, in these climates, care must be taken effectually to protect it, by thorough painting. Such a construction as a bridge, with wrought-iron girders, must be constantly painted and carefully protected from the influences of the climate, which possessed the peculiarity of an excessive degree of heat, combined with much moisture, the corroding effects of which, upon wrought-ironwork, were remarkably rapid.

Mr. J. WHITFIELD, in reply upon the discussion, for the Author, said with regard to timber, there was a great variety of wood in Brazil which would be useful and would endure for a long time under any circumstances; other descriptions under the most favourable circumstances would not endure for twelve months. There were some varieties of timber the outside of which was ex

ceedingly perishable, but the interior would last for a long time. He had known instances of timber, which had been in use for fifty years, both in and out of water. That was proved to be the case in some old buildings he had examined; and he found that some descriptions of timber would last sound for a long time. It was quite true that wrought iron when put under sea water rapidly became encrusted with marine shells, which protected it to a great extent but wrought iron when exposed to the atmosphere, near the coast, if not kept well painted, was very quickly corroded and destroyed. In the interior of the country, where the atmosphere was drier, ironwork properly painted would last as long, if not longer, than in England. It was a great mistake to suppose that the whole of Brazil was like that part of the country, near to the sea-coast. The hygrometric state of the atmosphere had a powerful effect upon materials near to the coast; but it was different in the interior. Some materials of construction might therefore be usefully employed in one situation, which would perish rapidly in another locality.

March 31, 1863.

JOHN FOWLER, Vice-President,

in the Chair.

No. 1,082.-"Structures in the Sea, without Cofferdams; with a Description of the Works of the new Albert Harbour at Greenock." By DANIEL MILLER.

Of late years a revolution has been going on in nearly all the branches of engineering practice. The application of scientific principles, the adoption of new constructive materials, and the development of modern wants, by the expansion of trade and commerce, have in some cases much altered the formerly received modes of construction, and in others rendered necessary the introduction of entirely novel methods.

Although harbour and dock engineering has participated in this change, there is no doubt still scope for improvement, in the scientific and economical construction of these works. And when it is considered how much the prosperity of a great maritime and commercial country depends upon the extent and efficiency of its docks and harbours, few subjects are deserving of greater attention.

The more immediate object of this Paper is to treat of the various methods of constructing the foundations of quay-walls, piers, or breakwaters, for the formation of docks and harbours in deep water; to describe works of this kind carried out on principles different from those usually practised; and to point out the further application of these principles to other works of a similar

nature.

The formation of these works has usually required the adoption of very expensive means; and an easy and economical mode of building such structures, so as to combine the various conditions necessary to insure solidity and capability of resisting the mechanical forces to which they are subjected, and also the destructive action of exposure to the elements, the boring of marine worms, or the corrosive action of salt water, has been hitherto a desideratum.

Several methods of founding works in deep water are at present practised; but there are objections to most of these systems, arising either from their expensive nature, or from defects in the dura[1862-63. N.S.]

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bility of the structures. The plans which have chiefly prevailed

are

Founding on piling carried up to about the level of low water;

Constructing within caissons or cofferdams; or,

Building under water by means of diving apparatus.

The first method has serious defects, both in deficiency of strength and of durability, as the piling is often insufficient to resist the lateral pressure from behind the wall, and the heads of the piles being exposed to the alternate action of air and water soon decay, when the weight of the wall above rapidly completes the failure of the whole structure. Of course where there are marine worms this mode is quite inapplicable. Instances of the failure of such works will occur to many. Referring to the River Clyde, for example, nearly all the older quay-walls of the harbour of Glasgow were built on this principle, and have given way from the decay of the piles, or have required very expensive repairs to keep them up; and at Port Glasgow Docks, the walls, which were also built on that system, gave way from the lateral pressure forcing them out, shortly after completion, greatly to the injury of that port.

The most usual mode adopted, where works of great solidity are required, is to resort to cofferdams, and to pump out the water from the enclosed space, so that the foundations and the walls may be constructed as on dry land. This is certainly most effectual, but it is at the same time generally expensive, and it is often not unattended with danger. In many cases, too, from the nature of the strata, it is almost impossible to form an effective cofferdam. The construction of cofferdams, moreover, frequently requires great engineering skill, besides involving vast expense; and when it is considered that they are only wanted for a temporary purpose, t must be conceded that it is an object of great importance, to devise some mode by which their use can be obviated, and solid and durable works can be executed without their aid.

The system of building under water by means of diving-bells and diving-dresses has been practised to a considerable extent, and the improved apparatus now used gives great facilities for this kind of work; but it is only applicable under particular circumstances, and it is also costly, besides being liable to cause delay in the progress of the work. The Dover Breakwater, at present in course of construction, is an example on a large scale of this mode of construction, but it is also an instance of the vast sums which may be expended on this system.

In bridge building, a great innovation has been made in the construction of the piers without the aid of cofferdams, and the