It seems likely that trigonometrical surveying may be carried on with less difficulty in future; for an Italian officer of engineers, Lieutenant Manzi, has proved that the triangulations can be photographed. It is possible to construct a camera geometrically arranged, and if the rays of light converging from distant points of view are intercepted, and marked on a diaphragm, it is evident that the angular readings obtained to such points would be identical in their bearings with the objects themselves. By such a camera, negative views of inaccessible ground can be faithfully taken, and the angles can be either plotted or calculated. Photography thus offers itself as a means whereby a difficult mountain country can be surveyed without risk, while for purposes of military recognisance its advantages are obvious.
For some time past attention has been directed towards steel-wire cables; and experiments recently made in Portsmouth Dockyard have clearly demonstrated their superiority over hemp and iron. Steel, as is well known, is more and more used in the building of ships, and, because of its tenacity and lightness, in their rigging; and now it seems likely to supersede the unwieldy hawsers and chain cables everywhere in use. With a chain the safety of the ship depends on the weakest welding; and when a single link parts, either from inherent defect or from a sudden jerk, everything parts, and the vessel drifts. A wire cable, on the contrary, gives notice, so to speak, of an approach to the breaking point. First one strand, then another, gives way, and still the cable holds, and it may happen that it will hold long enough to save the ship. Now that experiment has proved that a steel-wire cable is as flexible as the best hemp, that it is three times as strong, and does not cost more, the change from one to the other may be made with confidence. Another advantage is the lightness, for by making use of steel, about two-thirds of the usual weight of the cable is got rid of. Evidence of the strength is seen in the fact that a three-inch steel hawser did not break until the strain exceeded twenty-two tons, and that a strain of more than a hundred tons was required to break the six-inch.