turies that had elapsed since old London Bridge had been erected, the science of bridge-building had made but little progress in England. The principal structures of the sort were of wood. Trees, merely squared, were laid side by side, at right angles with the stream, supported on perpendicular piles, the roadway being planked over and covered with gravel. Old Battersea Bridge was an example of the primitive structures by means of which many of our wide rivers long continued to be crossed. Few were built of stone, and these, of a comparatively rude kind, were principally situated upon the main lines of road; but they were usually liable to be swept away by the first heavy flood. During the period referred to, however, the science of construction had made great progress in France, and from the practice of French engineers our best models continued for some time longer to be drawn. Hence, when the sanction of Parliament was at length obtained to a second bridge being built across the Thames, Labelye, the French engineer, a native of Switzerland, was employed to design and execute the work.

It will have been observed that the chief difficulty with the early bridge-builders was in securing proper foundations for their piers. A common practice was to sink baskets of small dimensions, full of stones, in the bed of the river, and on these, when raised above water, the foundations were laid. But where the bottom was composed of loose, shifting material, such as sand, it will be obvious that a firm basis could scarcely be secured by such a method. The plan adopted by Labelye, though considered an improvement at the time, was even inferior to the method employed by Peter of Colchurch in founding the piers of old London Bridge in the 13th century. For, clumsy though the latter structure was, it stood more than six hundred years, whilst Westminster Bridge had not been erected a century before it exhibited signs of giving way.

Labelye's method of founding his piers was as follows. He had a sufficient number of large caissons, or water-tight chests, prepared on shore, of such form as to fit close alongside of each other. They were then floated on rafts over the spots destined for the piers, where they were permanently sunk. The top of each caisson, when sunk, being above high-water mark, the masonry was commenced within it, and carried up to a level with the stream, when the timber sides were removed and the pier was left resting firmly on the bottom grating. The foundations were then protected by sheet-piling, that is, by a row of timbers driven firmly side by side into the earth all round the piers.

Westminster Bridge was originally intended for a wooden bridge, but the design was subsequently altered to one of stone, Labelye considering it necessary to have a great weight of masonry in order to keep his caissons at the proper level. To add to this weight the engineer added a lofty parapet, which Grosley, a French traveller, gravely asserted was placed there for the purpose of preventing the Londoners from committing suicide!

Not many years after Westminster Bridge had been opened, the London Common Council, in order to facilitate the passage of traffic across the Thames as near to the centre of the City as possible, applied to Parliament for powers to construct a bridge at Blackfriars; and the requisite Act having been passed, the works were commenced in 1760, and finished in 1769. The architect and engineer of Blackfriars Bridge was Robert Mylne, and a noble piece of masonry it was. it was. The principal new feature in this structure was the elliptical arch,' which Mr. Mylne

1 The disadvantage of the semicircular arch was that, though selfcontained, it necessarily led to a great rise in the road over the bridge, which was steep at both sides. By means of the flat elliptical arch this disadvantage was obviated, and more water-way was afforded, with less rise

in the bridge. But greater science was required to construct bridges of this sort, as the strength mainly depended upon the abutments, which bore the lateral pressure. When the span was extensive, and the arches of considerable flatness, the greatest care was also required in the selection of

was the first to introduce in England. The innovation gave rise to a lively controversy at the time, in which Dr. Johnson took part, in opposition to Mr. Mylne, and in support of his friend Gwyn, who was the author of a rival plan. Boswell, in his Life of Johnson,' defends the design of Mylne, his countryman, and adds, "it is well known that not only has Blackfriars Bridge never sunk either in its foundation or in its arches, which were so much the subject of contest, but any injuries. which it has suffered from the effects of severe frosts, have been already, in some measure, repaired with sounder stone, and every necessary renewal can be completed at a moderate expense." This was written in 1791, only twenty years after the bridge had been opened; and, though it may have been true then, it is so no longer. When the numerous heavy piers of old London Bridge were removed, the velocity of the unimpeded tide, sweeping up and down the river twice in every twentyfour hours, and the consequent increased scour of the water along the bottom of the Thames above bridge, soon began to tell upon the foundations both of Blackfriars and Westminster Bridges; and they exhibited the unsightly appearance of numerous props and centerings to prevent the further subsidence of their foundations. Hence Labelye's bridge at Westminster has already been removed, and the probability is that before long Mylne's bridge at Blackfriars will share the same fate.

the stone, which must necessarily be capable of resisting the severest compression. Mylne overcame these various difficulties with great ability; and

had not the foundations of the structure proved defective, Blackfriars Bridge might have stood for a thousand years and more.

CHAPTER III.

WILLIAM EDWARDS, BRIDGE BUILDER.

THE difficulties encountered by the early bridge builders cannot be better illustrated than by a brief account of the life of William Edwards, the architect of Pont-yPrydd, a remarkable work erected at Newbridge, in South Wales, about the middle of last century.

Edwards was born in 1719, in a small farm-house in the parish of Eglwysilan, in Glamorganshire. His father died when William was only two years old; but his mother, who was an industrious, well-doing woman, kept on the farm, and piously and virtuously brought up her family. William's literary culture was confined to Welsh, which he could read and write from his early youth; but as he grew older he also learnt to read and write English, though more imperfectly. He had the character of being a very obstinate, stubborn, and self-willed boy-qualities which, under the guidance of rectitude and integrity, became developed into inflexible courage and resolution in his manhood. Until eighteen years of age he was regarded as a wild, headstrong fellow, with little promise of good in him; but he was gradually tamed and disciplined by hard work, and as he grew older he became thoughtful and sedate even beyond his years.

Edwards's ordinary employment was common farmwork; but at the same time he was a diligent self-educator, taking lessons in arithmetic from a neighbour in the evenings. It happened that, in the ordinary course of affairs, he had occasion to repair the dry stone walls about the farm. He took particular pleasure in this kind of work, and very soon became remarkably handy at it;

but he always longed to do better. Some masons having come into the neighbourhood to build a smithy, Edwards would occasionally leave his farm-work and take his stand in the field over against which the masons were employed,

eagerly watching them while they worked. He admired the way in which they handled their tools and prepared the stones for the building. One thing that he particularly noted was the way in which they dressed the rough blocks by means of the pointed end of the mason's