Leaving this question to the experts, we add, in passing from the subject, that the orbital velocity of one of the moons is seventy-nine miles a minute; of the other, fifty miles; and that their discovery has enabled astronomers to determine the mass of Mars, and thus settle what has been to them an important and long-standing problem.
As a reverse to this astronomical triumph, we have to record the death of Le Verrier, an astronomer pre-eminent among the astronomers of the century, with such insight and such capacity for work as have rarely been equalled. He will be known through coming ages by his theory of the motions of the planets, and the tables founded thereon; for provided with these, astronomers all over the world are enabled to carry on their work with an accuracy hitherto unapproachable, and to widen its application. France has lost one of her greatest sons, and Science one of her most distinguished elaborators; but he lives in his works, and through them will continue to guide and instruct the mariner, the astronomer, and the physicist.
Mr Stanley's exploit in turn settles an interesting geographical question, for embarking on the Lualaba, he followed that river down to the Congo, and the Congo down to the sea. Thus the drainage of the lake-region of Central Africa finds its way into the Atlantic. The voyage proved fatal to some of the party through conflict with hostile natives, and accidents among the cataracts, which on the equator impede navigation for a distance of thirteen miles. The river is described as from two to ten miles wide: it drains an area of one million four hundred thousand square miles; and now with the Congo and the Nile, Africa may claim two of the largest rivers in the world.
It often happens in dark weather that the position of a ship can be ascertained only by sounding; and when near the land, the soundings should be frequent if danger is to be avoided. But as the depth cannot be accurately measured without bringing the ship to a stand-still, the seaman is apt to prefer risk to loss of time; and the consequence is at times—a wreck. Sir William Thomson, to whom navigation is indebted for an important improvement in sounding apparatus, has recently proved by experiment that by adding thereto a chemical appliance the sounding may be taken while the ship is in motion. This appliance consists of a copper tube, attached to the lower end of the sounding wire, and inclosing a slender glass tube, and a small quantity of sulphate of iron. As the tube descends, the pressure of the water forces the sulphate into the glass tube: it leaves a stain on the glass; and according to the height of the stain, as indicated on a scale, such is the depth of the water. We are informed that this ingenious instrument has been tried on board the Minotaur with satisfactory proof of its 'absolute accuracy and extreme handiness.'
H.M.S. Téméraire is appropriately named, for she is big enough and heavy enough to do battle with any antagonist that may venture to face her in the Mediterranean, whither she is bound. The engines are 7697 horse-power. No wonder that the mighty vessel when under way pushes up a ten-foot wave at her bow! The diameter of the principal cylinders is seventy inches; of the crank shaft, twenty-two inches; from which an idea may be formed of the bulk of the ponderous mass. To reduce the weight as much as possible, wrought-iron and brass are largely used in the construction of the engines and fittings, in place of cast-iron, so that in the condensers there are more than eleven thousand brass tubes, which make up a cooling surface of fourteen thousand square feet. To assist the movements and facilitate the working of this giant among war-ships, there are on board thirty-four small engines, thus distributed: two turning, two starting, four feed, two circulating, four fan, two bilge, one capstan, one steering, four pumping, four ashes lifters, two hydraulic gear workers, one torpedo reservoir charger, one to work the electric machine which feeds the lights on the bridge, and four others. In all this there seems something of complication; but we may hope that everything will work well even in the worst of weather, so that the ship may justify her name and the merits of her builders.
The Iron and Steel Institute held their annual meeting at Newcastle-on-Tyne, where, and in the neighbourhood, the manufactures and other mechanical operations abound in which the members take most interest. That these are mines, coking furnaces, brick-works, iron-works, and foundries, may easily be imagined. One of the papers read shewed that cast-steel could be produced without compression, and as readily as cast-iron; which if confirmed by further experiment, will prove of great value in the manufacture of heavy cannon.
In a visit to Sir William Armstrong's works at Elswick, the members saw the welding of coils for guns under the great steam-hammer, which weighs thirty tons, and falls upon an anvil of one hundred and twenty tons, with a stroke of twelve feet six inches; and yet so perfect is the hydraulic moving machinery, that it can be easily worked by one man. The four cranes too by which the ponderous masses of red-hot metal are lifted, are 'under the command of one man, who can sling them right and left, or move the load up or down just as he pleases without moving from his post.' Another example of what can be done by water was shewn at the swing-bridge across the Tyne, which has four spans of about one hundred feet each. The portion which opens weighs fifteen hundred tons. 'The hydraulic machinery for actuating it, is contained in the hollow pier which forms the pivot on which it turns. The pier is surmounted by a watch-tower, in which are the levers for opening and shutting the bridge. It takes just one minute to swing the bridge from its closed position across the river to the open one in line with the stream.'
Mechanists have pointed out that water-engines use the same amount of water when merely driving themselves (which is next to doing nothing) as when exerting their entire power. If it be true that there should be a proportion between the amount of work and the quantity of water, this, as we are informed, is provided for by Hastie and Company of Greenock in an invention by means of which an automatic lengthening or shortening of the stroke of the engine takes place, in accordance with the work to be done. No sooner does the engine become, so to speak, aware of the demand on its power, than it immediately adapts itself thereto without external assistance.
To revert to the Institute: A description was given of the coking coal-field of South Durham; it is thirteen miles long by eleven miles wide, and assists in supplying the present demand for fourteen and a half million tons of coke yearly. At one of the collieries there used to be a waste of three hundred tons of coal every week; but now by means of improved coking ovens, and intercepting the waste heat, this loss is prevented. It is found too that the large deposits of inferior coal can be utilised, by crushing, washing, and then coking: a very important fact, for there is in all our coal-fields a large breadth of coal which has been hitherto rejected as worthless, but which will now be worked and converted into coke.
A paper was read which shews that ways are opening for the utilisation of slag: it is now converted into bricks, cement, mortar, concrete, glass, and cotton or wool. This wool is an excellent material for covering boilers and pipes to prevent waste of heat. Four million bricks have been made, which looks promising.