A VALUABLE addition has recently been made to MANBY'S Mortar Life-Apparatus, by the ingenuity of Captain K. B. MARTIN, the well-known Harbour-Master of Rams- gate. That apparatus having been supplied by the Commissioners of Ramsgate Harbour to their steam-tugs, and placed also on their pier, Captain MARTIN made it his business to practise his "men in the use of the same, and to make various experiments with it to ascertain the ranges* f the shot at different elevations, and under various circumstances, In the course of these experiments, the idea occurred to him that there might often be a great advantage in throwing a line attached to a floating body instead of an iron shot, whether from a vessel to the shore, or the reverse, or from one vessel to another; so that a Manilla line, which would not sink by its own weight, might, instead of being sunk by the shot, be kept floating on the surface of the water. " I therefore," he states, in a paper on the subject, in the Nautical Magazine, for January 1856, " de- termined to try the effect of cones of wood of different densities; and the best of which I find to be the gnarled or knotted elm, which resists the concussion without splitting, and which my turner furnishes at Is. 6rf. each, of 5J inches diameter, and 9 inches length, these being the dimensions of the largest iron projectile fitted to the bore of the mortar." Captain MARTIN found that he could throw a wooden cone as above described, weighing 4 Ibs., with a charge of 6 ozs. of powder, 60 yards against a fresh gale of wind, and before the wind 160 yards. The extreme range of an iron shot with the same line attached and an equal charge of powder he found to be 214 yards.

It is not proposed by Captain MARTIN to substitute wooden cones for iron shot, but to employ them as an auxiliary to the latter, since, under many circumstances, they would appear to be more suitable.

Their advantages seem to be— 1st. When fired from the shore to a wreck, over an upset boat, or over drown- ing persons in the water, the floating pro- perty of the wooden shot would cause the line to be much more easily grappled with by those for whose aid it was intended, if the direction of tile shot did not place the line immediately over them, and within their reach.

2nd. Owing to its flight not being so rapid as that of an iron shot, it is less liable to break the line, to the loss of the shot and delay of valuable time, whilst for the same reason it is less likely to injure persons on board a wreck, as they could more readily see and avoid it when coming immediately towards them. It could only, however, be available for carrying a line from the shore to a vessel when the former was sufficiently steep to allow of the latter driving within a short distance of it.

3rd. If fired from a wrecked vessel to the shore, its diminished velocity of flight and reduced weight would be less likely to injure persons on the land, whilst, if it fell short of the shore, it would not bury itself, but be drifted within a short distance of the beach, so that those assembled there might be able to grapple it 4th. Similar advantages, but in a still greater degree, would attend its use in com- municating from one vessel to another at sea, when, as Captain MARTIN observes, a disabled ship might often, through its instru- mentality, be taken in tow.

As the wooden shot are so cheaply made, as a matter of economy alone, they would very usefully be added to every MANBY'S Mortar Apparatus; and we hope to learn that they have been provided by the Board of Customs at all those Coast-guard Stations which are furnished with the mortar. It would, no doubt, also, as recommended by Captain MARTIN, be a most important ad- vantage if the MAS BY Apparatus were furnished to our merchant vessels generally, more especially to emigrant and passenger ships.

The mortar would, in addition to its legitimate use, be of service as a signal gun, and might, perhaps, even be employed as a weapon of defence under some circumstances.