IN our last number we considered the question as to the application of steam- power to Life-boats, and pointed out what we considered the insuperable difficulties in the way of its use. At the same time, however, who indicated that greater power than can be applied by the use of oars would be a great advantage, although the failures of Life-boats to attain their object were unfrequent, as compared with their numberless successes.

The question then arises, can manual labour be applied in any more advantageous manner than by the use of oars.

In considering this question, we must, at the outset, remember that no actual in- crease of power can be obtained by the use of any machinery, and that all which the science of mechanics can do for us is to vary its application, so that whatever we ! gain in velocity we must lose in power, j and whatever we gain in power we must i lose in speed.

There are only two principles of propulsion applicable to vessels floating on ; the water's surface, viz., that obtained by ! external pressure on the vessel by the wind, and that effected by a blow or pressure on the water exerted from the , vessel itself, as by the paddle, the screw, the turbine wheel, and the oar, unless we include tracking or towing a vessel through | a canal or along the bank of a river by horses or other animals or men.

To proceed from the land to sea, we have then only the choice of the two first- named principles, the second of which is that which is the subject of our present consideration. In each of the modes of applying it, whether by the paddle, screw, turbine wheel, or oar, or by any other that can be devised, the water is used as a fulcrum, and the mechanical law of action and reaction is the source of motion, the reactionary force from the blow or pressure giving, what is, in reality, a backward motion to the vessel, just as the rebound of a ball from a wall or other plane surface is a backward motion caused by a force imparted to it in an opposite direction.

In exerting that force, of any given amount, such as the strength of ten powerful men, all we can do is to enable them to apply it in the most convenient manner and with as small an amount of loss from friction as possible.

In a former number we stated, that although one of the most ancient, if not the most ancient, instrument of hand propulsion, an oar is still the simplest and the most effectual, and that we doubted if it would ever be superseded. At the same time, since the notion that greater force can be exerted and greater speed obtained by rotary instruments, such as the paddle and screw, worked by hand- power, than by an oar, is still tenaciously held and persistently advanced by inventors and others, and as the propulsion of Life-boats, on the success of which life or death so often depends, is a matter of special importance, the subject ought, undoubtedly, to receive the fullest consideration, and any plans which should hold out the least probability of success, should be practically tested.

We are led to these remarks by the introduction during the present year of a j ship's Life-boat, invented and patented by a Mr. HARRIS, of Gravesend, which was tested alongside the Worcester training ship, in the Thames, on the 5th of May last, which was favourably reported on at the time, and an engraving of which we here insert, taken from a block furnished by the inventor.

Like all inventors, Mr. HARRIS is most sanguine as to the value of his plan, the principle of which is however no novelty, as many persons have before advocated the use of screws and paddles worked by hand-power, in preference to the oar, and of covered, in preference to uncovered, Life-boats, which two principles are the leading features in this one.

We will not here pronounce an opinion on Mr. HARRIS'S boat, which, like every- thing else, must be put to the test of experience before its value can be known; since, however, it has gone beyond the terminal stage of the majority.' of inventions, viz., that of a model or drawing, it is but justice to him to state, that he has not only built a full-sized boat and put it through a harbour trial alongside the Worcester, to show that, like the Life- boats of the NATIONAL LIFE-BOAT INSTITUTION, it will self-right if upset, but that lie has proceeded in it to the Goodwin Sands in a strong breeze. He states that he tried it both under oars and with the screw, each being worked by 4 men, and that he was able to make progress against both wind and sea with the screw when he could make none under oars.

Of course, the whole value of such a trial would depend on the force of the wind and sea at the time, and as to whether the oars were so placed and fitted that they could be as advantage- ously used as in any good rowing boat, which we have no means of knowing; we therefore relate the circumstance on Mr. HARRIS'S authority alone. The boat in question is small, but of useful size for an ordinary merchant vessel, being 20 feet long by 6£ feet wide and 3 feet 4 inches deep.

Having said this much of this particular boat, we will proceed to comment on the general principle, and to state what appear to us to be the relative advantages and disadvantages of covered and uncovered boats, and of propulsion by oars and rotatory machines.

As for back as 1850, when the then DUKE OF NORTHUMBERLAND offered a prize of 100?. for the best plan of a Life-boat, the late Mr. OLIVER LANG, at that time one of our chief naval architects, sent, to compete for it, a model of a boat, which, like Mr. HARRIS'S, was covered over or roofed, and was to be propelled by paddles worked by hand power.

Mr. LANG'S reasoning on the first head was that, as a boat ordinarily upsets from the admission and settlement of water on one side, with consequent loss of stability, all that was required to counteract this danger was to exclude all water from within the boat, and so to arrange and secure her ballast that, however much she should be thrown on one side, or even if overturned by the sea, she should always recover her natural position. This theory was undoubtedly correct, and the desired effect was readily accomplished; and it is, we think, worthy of consideration whether, in passenger ships going on distant voyages, one or more of the Life-boats might not be covered over or partially so. If, how- ever, entirely covered over, it would be indispensable that a sufficient portion of the roof-deck should be portable and only require to be in its place for safety and protection in gales of wind; for it is evident that to be for any length of time shut up in so small a space in a necessarily crouching or reclining position, and with probably insufficient ventilation, would but be an illustration of the pro- verb that a " remedy may sometimes be worse than a disease." In coast Life-boats, even if it could be shown that such a boat was safer than an open one, we think it very questionable if the men who work them would consent to be shut up under cover, with no opportunity of seeing and judging for themselves of their whereabouts and of the extent of any danger that they might be called on j to encounter. Just as most persons are, , naturally, more apprehensive of danger in the dark, when it maybe invisible, although , close at hand; so, when their boat was ' thrown nearly perpendicular by a heavy '• broken wave throwing up the bow or stern,! or nearly rolled over by a broadside surf, ; a Life-boat's crew might imagine that the 1 next moment they might be dashed to pieces on a rock, or that they might be hopelessly drifting into a fatal position from which they could never extricate themselves.

There would probably also be often great difficulty in getting a wrecked crew safely on board, through a small open hatch in the roof-deck of the boat. We have dwelt this much on the peculiarity of roof-covering since it is a general accompaniment of plans for propelling Life-boats by paddles or screws. We will now consider the question of propulsion ; and it will be sufficient to enumerate the special advantages of an oar, to show that any other hand-propeller entering the " Lists " to contend with it will meet with a very formidable competitor.

I. " Oars."—The peculiar advantages of oars are as follows: 1st. They are constantly in the hands of our coast boatmen, as well as of the crews of ships, and their management is, therefore, not only tho- roughly and practically understood, but every muscle of the body which has to be brought into play is strengthened by daily use, which two advantages are undoubtedly of the very highest importance.

2nd. The friction in working them is very slight when they are properly fitted.

3rd. In the hands of practised rowers they can be accommodated to the motion of the sea, so that they can always be used at full power.

4th. If broken, they can be readily re- placed, spare ones being kept on board.

5th. From their oblique stroke, on first immersion, the oars towards the bow and stern can be used with much effect in keeping a boat's head up to the sea and in turning her round, when required, in a short space. This also is a most important advantage.

On the other hand, their disadvantages arc: 1st. That the force which has to be used to make the back stroke and place the oar-again in position is a direct loss, allied with which is tho loss of momentum consequent on tho motion being backwards and forwards instead of being continuous.

2nd. When out of the water they must hold more or less wind, which is a disad- vantage when rowing against a fresh gale.

II. " Sotary Propellers."—Their chief if not only advantage would be, that the motion being continuous the whole of the force exerted is in one direction, round an axis, and that by the aid of a weighted or " fly-wheel" they may be made to retain their momentum, which would assist to carry them over any momentary extra resistance : as, for instance, that of the blow of a heavy-sea, and over those parts of their circuit when the men working them could not employ their strength to advantage.

Their disadvantages are: 1st. That the men who would be alone available to manage them, would be unaccustomed to the work of turning the handle of a winch, and would not use their strength so advantageously as in rowing an oar; whilst, if they exerted themselves continuously, round the whole circle, the labour would | be very exhausting, and they would soon succumb from fatigue, especially as they would be working in a confined atmosphere, if in a covered boat.

2nd. They would be powerless to keep a boat's head up to the sea when both wind and sea were very high and on one bow.

3rd. The friction in working them would ! probably be greater than that of an oar.

4th. If the shaft of the screw or any other part of the machinery should get broken or out of order, the boat would lie at the mercy of the wind and waves.

5th. In the case of paddles they would work at great disadvantage, consequent on the violent motion of the boat from side to side; since the paddle on one side would often be spinning round in the air whilst the other would be too deeply immersed. A screw would likewise be frequently out of the water, from the pitching or longitudinal motion.

To return, however, to Mr. Harris's boat.

His engraving has, perhaps, rather too much the appearance of a first and -second class cabin; which social distinctions would be entirely lost sight of at a moment j of common danger; but his motive, no i doubt, has been to show that even a delicate female, in such a boat, would not only be protected from the inclemency of the storm, from cold and wet, but that she ; might even be able to lie in a reclining position, in comparative rest and comfort.

As stated above, we pronounce no opinion on the practical value of such a boat, but introduce it to our readers as involving principles deserving careful consideration.