usually exhibiting a diameter of only 1 centimetre, but occasionally some are found of two or three times that size. As a rule these bubbles are very ephemeral; now and then, however, it happens that some may be caught along with a quantity of water in a small beaker glass, and on the mercurial bubbles bursting, it will be seen how very small a quantity of mercury these bubbles consist of. Professor Hofmann mentions that he saw this experiment first exhibited in the lecture-room of the Royal College of Chemistry, London, when, twenty years ago, Professor Melsens, from Brussels, was on a visit there.

Caustic baryta is likely to become of considerable use for industrial purposes. M. Nickles has described its mode of preparation. It appears that four operations are required:-(1) Conversion of native sulphate of baryta into sulphide of barium; this is effected in a continuous manner, in a peculiarly constructed furnace, the sulphate being previously mixed with a reducing substance; (2) the conversion of the sulphide of barium into hydrate of baryta, by means of hydrated oxide of zinc; (3) dehydration of the hydrate of baryta by ignition along with sawdust; (4) regeneration of the substance which has served for the desulphuration of the sulphide and obtaining of sulphur.

M. E. Underhold states that the hardest steam-boiler incrustations are formed when the quantity of carbonate of lime amounts to from 20 to 25 per cent. of the entire mass. He has found, by an experience extending over several years, that some kinds of clay when suspended in the water contained in steam-boilers, prevent the particles of carbonate and sulphate of lime dissolved in the water, even if the latter is very hard, from clinging together and becoming fixed to the sides of the boilers, forming there a hard incrustation. A series of experiments, made on purpose and continued for a sufficient length of time to yield a reliable result, has fully proved that the addition to the feed-water of the steam-boilers of fatty clay, especially that known as fuller's-earth, entirely prevents boiler incrustations, even where, of necessity, very hard water has to be used as feed-water. A loose soft mud is deposited as soon as the motion of the water due to the boiling ceases on cooling. This mud readily runs off on opening the valve of the boiler.

Some valuable sulphur deposits have been discovered in the island of Saba, Netherlands, West Indies. The rock composing almost the entire formation of Saba is trachytic porphyry, which contains glassy felspar and hornblende in crystals, disseminated through a dark reddish-coloured vase. The sulphur deposit is located on the northern part of the island of Saba, and extends for a distance of more than a mile along the sea line. The stratum of

sulphur varies in thickness from 15 to 50 feet; its elevation above sea-level varies from 45 to 200 feet. This island has a surface of about 9 English square miles, or 5760 acres, and contains 1794 inhabitants.

6. ENGINEERING-CIVIL AND MECHANICAL. The Suez Canal.-The past quarter will long be memorable in the annals of Civil Engineering for the completion and successful inauguration of one of the most wonderful works of modern times. The Isthmus of Suez Canal, just completed, is, however, the realization of no modern conception. The idea of traversing that isthmus, or at least the greater portion of it, is so ancient that the original author of it cannot now be named; but evidences remain to show that, at some very remote period, a canal really did exist between the river Nile and the Red Sea. As far as can be ascertained it was undertaken by Necho, about six centuries before the Christian era, and subsequently completed by Darius. There exists amongst ancient writers some difference of opinion as to the precise character of the canal and its exact route, but there can be no doubt that a canal was once made, extending from the Nile to the Bitter Lakes, a distance of about thirty-four miles, which, being filled with fresh water by the rising of the Nile, was navigable for at least such portion of the year as the Nile was in flood: it is also certain that a smaller canal was continued from the Bitter Lakes to the Red Sea, near Suez. These works, which for many centuries had been allowed to fall into decay, were restored about A.D. 649 by the Caliph Omar; but instead of the restored canal joining the Nile, near Bubastis, it curved southward to Cairo, and was named the Canal of Cairo.' This canal appears to have continued open until about the year A.D. 767, affording means of water communication between the Nile and the Red Sea. Subsequently to the above date there do not appear any records of its existence; but at the latter part of the last century the Emperor Napoleon Bonaparte, during the time of the Egyptian expedition, caused a complete survey of the old canal and of its route to be made by M. Lepère. That officer's report was dated in 1799; but in consequence of the withdrawal of the French from Egypt no further action was taken in the matter.

The next report on the subject which deserves notice was that of Captain Chesney, of the Indian army, in 1830, who proved the perfect practicability of the project, and his views were subsequently verified by surveys undertaken under Robert Stephenson. For many years previously Linant Bey had considered the project of cutting a navigable canal across the Isthmus; and in 1845 an

association was formed with the view of carrying the work into effect. Prior to that date, however, M. de Lesseps had formed his conclusions on this subject; and in 1854 he suggested his ideas to Said Pacha, by whom the project was warmly entertained. A commission, composed of the principal engineers of Europe, was convened to examine the scheme, who visited the site in November, 1855, and in January following they submitted their report, in which the undertaken was represented as easy of accomplishment and certain of success, and the estimated cost was then set down at 200,000,000 francs. A concession was shortly afterwards given to M. de Lesseps for the construction of the canal; and after further careful investigations the works were set in hand, the completion of which was celebrated by the opening of the entire canal on Wednesday, the 17th November last.

The course of the canal is from Port Said, on the Mediterranean, through Lakes Menzaleh and Ballah, after which it is cut through some high ground at El Guisr, which separates Lake Ballah from Lake Timsah. Between the latter lake and the Bitter Lakes lies also a length of high land, extending from the shore of Lake Timsah to Serapeum, after which the canal enters the district of low, swampy land, known as the Bitter Lakes. It then reaches high ground once more at Chalouf, and for the remainder of the distance to Suez passes through high land in deep cuttings. The length of the canal is about 100 miles. The total expenditure upon the canal has been 434,000,000 francs; but according to a statement recently published the net cost, after allowing for the present value of plant, &c., has been 216,000,000 francs.

Blackfriars Bridge. In addition to the above great international work, there have been completed, within the period under review, two important engineering projects within the city of London, namely, the reconstruction of Blackfriars Bridge across the Thames, and the erection of a viaduct across the Holborn Valley.

Old Blackfriars Bridge was first thought of in 1754, at which date there existed no means of communication across the Thames between London and Westminster Bridges; and in 1756 an Act was obtained for the erection of a bridge across the Thames in the neighbourhood of Fleet Ditch. On 26th April, 1760, a contract was entered into with a Mr. Phillips for the construction of a bridge for 110,0007., from the designs of Mr. Robert Mylne. On the 31st October, in the same year, the first stone was laid by Sir Thomas Chitty, Lord Mayor, and the bridge was opened to foot passengers on the 19th November, 1766. It was not, however, until the 19th November, 1769, that it was finally completed and opened for wheel traffic. On the 8th June, 1864, old Blackfriars Bridge was closed, and the traffic diverted over a temporary

wooden structure erected by its side. The design for the new bridge was prepared by Mr. J. Cubitt, and the estimated cost was 269,0007. Space will not admit of a detailed description of this bridge, which was opened by the Queen in state on the 6th November last.

Holborn Viaduct.-On the same date the Holborn Viaduct was completed and declared open to public traffic. This important work, extending from the top of Holborn Hill on the west to the top of Skinner Street Hill on the east, crosses over the ancient valley of the Old Bourne, affording a straight line of communication where two steep hills previously impeded the traffic. The works have been carried out from the designs of Mr. Heywood, the city architect, at a total cost of about 2,000,0007.

PROCEEDINGS OF SOCIETIES.

Institution of Civil Engineers.-Considerable indignation has been recently aroused amongst the members of the engineering profession in England and India, in consequence of a Circular Order issued by the Government of India, from which it was distinctly to be inferred that the practice of accepting bribes from contractors and others was recognized by the profession in England. At the first ordinary meeting of the Institution, on the 9th November, the President reported that on receipt of a copy of the Order in question, a meeting of the Council took place, at which a series of resolutions were passed totally repudiating the calumny, copies of which were forwarded to the Secretary of State for India. At a deputation of the Council, which subsequently waited upon the Duke of Argyll, his Grace promised to forward the representations of the Institution to the Government of India, and to call for some explanation as to the circumstances which led to the publication of the Order; and in a subsequent letter to the President of the Institution, his Grace declared that "he regarded with implicit confidence the indignant repudiation of the Institution of any recognition of the practice referred to in the notification."

Society of Engineers. The principal paper which has been read before this Society in the present Session, is one by Mr. P. F. Nursey, on "English and Continental Intercommunication." After referring to the present defective means of transit across the British Channel, the author briefly alluded to a few impracticable suggestions which have, from time to time, been proposed for the purpose, and then referred more in detail to those projects which have been put forward by experienced engineers. These may be divided into three classes, namely:-1. Those for tunnelling under the bed of the sea between England and France. 2. Schemes for carrying a

railway through submerged tubes laid at the bottom of the sea; and 3. For the improvement of the passage-boats, or, in other terms, the construction of a huge Steam Ferry between the two countries. A fourth class of projects may be enumerated, namely, those having for their object the construction of a high-level bridge across the Channel, but such hardly come within the category of practical schemes. That which can be constructed at least cost and with most expedition is the Channel Ferry project, and this we are inclined to think will, for the present at least, be found the most practical solution of the difficulty.

New York Society of Practical Engineering.—At a meeting of this Society, on 13th October last, a most useful and practical paper was read by Mr. C. Williams, C.E, on "Railway Accidents and the Means of Prevention." In the absence of wooden tio sleepers, the author advocated the laying of rails upon sleepers bedded upon sand confined in trenches formed either transversely or longitudinally with the track. The importance of securely attaching the rails to the substructure was dwelt upon; and, lastly, improved fish-joints and methods for avoiding the breaking of railway carriage axles were discussed, and the methods for effecting such means of security were dwelt upon at some length.

LITERATURE.

The Theory of Strains in Girders and similar Structures,' by Bindon B. Stoney, B.A.-The first volume of this work appeared three years ago. The present volume treats of the subject of girders under compression and in tension, as well as elasticity, temperature, and the practical designing and estimating of girder-work; and in the former part of the volume numerous references are made to the experiments carried out by Mr. Kirkaldy and Mr. Hodgkinson. As a text-book for practical engineers this will be found a useful work, but it would be impossible to enter fully into its merits within the space to which we are limited.

'A Practical Treatise on Concrete, and How to make it; with Observations on the Uses of Cements, Limes, and Mortars,' by Henry Reid, C.E.-At the present day when the use of concrete and cements is being so largely introduced into almost all engineering works, a more perfect knowledge of their properties is a subject much to be desired, and every fresh information coming from a reliable source is much required. During the earlier period of the introduction of concrete, which, in this country, is attributed by General Pasley to Sir Robert Smirke, it was regarded as being only fitted for foundations, or hidden work of a similar kind; but of late years that material has acquired a higher standard, and is now Longmans, Green, & Co., London. † E. and F. N. Spon, London.

*

VOL. VII.

I