made by the Association, and by Mr. W. Harding; and he presents the results in the following Table.

Mr. Russell remarks that the experiments show not only a great amount of resistance at high velocities, but likewise a great variation and anomaly in the results. He describes the resistance as consisting of three elements. Firstly, the friction of the axles and wheels, as an ascertained quantity, equal in the best carriages to 6 lbs. per ton of the train. Secondly, the resistance of the air; which, acting on a solid body such as a railway train, he regards as much less in amount than that inferred by Smeaton, from experiments on thin plates. And, thirdly, a large amount of resistance, increasing with the velocity of the train, and amounting, at ten miles an hour, to about 3 lbs. per ton, at thirty miles to 10 lbs., and at sixty miles an hour to 20 lbs. per ton; and which Mr. Russell ascribes to the concussions, oscillations, frictions of various kinds, &c., which are produced at high velocities.

Mr. Russell has constructed a formula compounded of these resistances, the comparison of the results of which, with those of the actual experiments, is shown in the Table; but the great anomalies observable at the various velocities remain yet unexplained, and appear incapable of being accounted for on any theory. Much is probably due to the combined action of inaccuracy in construction, and variation in the quality of the materials

employed. A doubt may likewise be suggested whether, in practice with heavy trains, the quantity of the first-named element of resistance, the friction of the axles, &c., is constant at all velocities.

New Sand Cement.

A metallic sand cement, of great hardness and tenacity, has been lately used on the London and South-western Railway and elsewhere, in forming mortar and concrete. The sand is brought from Swansea, and the proportions of the cement are,for mortar, the metallic sand, ordinary sand, and lime, in equal quantities; for concrete, metallic sand 1 part, lime 1 part, gravel 6 parts. The iron contained in the metallic sand becomes disseminated through the mass, and acts as a firm bond to the whole composition.

GAUGE OF RAILWAYS.

The experiments instituted by the advocates of the broad and narrow gauge, respectively, with the object of testing their respective merits as to speed and power, have not led to any satisfactory conclusion. The direction of the wind, the state of the rails, and the inclination of the road operated so variously during the trials, as to destroy all uniformity in the conditions of the several experi

ments.

Mr. Bidder, in his report on the recent gauge experiments, gives the following results:—

The friction of air through tubes, Mr. Bidder observes, is tolerably well ascertained: it appears that, with a pressure of 04 lbs. per inch, the velocity of the air through the long tubes of the A engine used in the narrow gauge experiments was 16 miles per hour; and through the shorter tubes of the Ixion 18 miles per hour.

Opinion of Mr. W. CUBITT on Uniformity of Gauge, (Evidence before Select Committee of the House of Lords.)

Proposes a 6-feet gauge, the alteration to which would cost between £500 to £1000 per mile.

Says that the bridges and tunnels on the existing narrow gauge railways are wide enough to admit of rails 6 feet apart, the only alteration necessary in the carriages being that of bringing out the wheels 6 or 8 inches each side, as the carriages themselves are already wide enough, and the wheels would still be under the body of the carriage.

The enlarging this gauge to 6 feet would make a better gauge, and enable them to bring the centre of gravity of the engine lower, and allow larger engines than can now be used with safety upon the narrow gauge.

Long engines (as long as 20 feet) may be made to run with very large driving wheels, and go safely round curves, by using what is called in America a "Bogy Carriage," viz. supporting the engine on