On the extraordinary effects of an Earthquake. 359 water around hissed as if hot iron was immersed in it ;' immense quantities of air-bubbles rose to the surface, the gas from which was offensive, resembling, to use my friend's phraseology again, rotten pond-mud.' Numbers of fish came up dead alongside; the sea, before calm and clear, was now strongly agitated and turbid, and the ship rolled about two streaks, say fourteen inches, each way. A cry of there goes the town,' called my friend's attention towards it: a cloud of dust, raised by the agitation of the earth and the fall of the houses, covered the town from view, whilst the tower of the garrison chapel, the only object visible above the dust, rocked for a few seconds, and then fell through the roof; and, from the high perpendicular rock at the north end of the island of St. Lorenzo, a slab, supposed thirty feet thick, separated from the top to the bottom of the cliff, and fell with a tremendous noise into the sea. The wharf or pier was cracked three parts across, showing a chasm of eighteen inches wide; the chronometers on shore, except those in the pocket, and most of the clocks, stopped, whilst the rates of chronometers on board were in many instances altered. A great number of lives were lost, amongst which were four priests, killed in the churches, one of them by the falling of an image, at whose base he was at prayer.

"The Volage's chain cables were lying on a soft muddy bottom, in thirty-six feet water; and, on heaving up the best bower anchor to examine it, the cable thereof was found to have been strongly acted on, at thirteen fathoms from the anchor, and twenty-five from the ship. On washing the mud from it, the links, which are made of the best bolt or cylinder wrought-iron, about two inches in diameter, appeared to have undergone partial fusion for a considerable extent. The metal seemed run out in grooves of three or four inches long, and three-eighths of an inch diameter, and had formed (in some cases at the ends of these grooves, and in others at the middle of them) small

spherical lumps or nodules, which, upon scrubbing the cable to cleanse it, fell on the deck. The other cable was not injured, nor did my friend hear of any similar occurrence amongst the numerous vessels then lying in the bay. The part of the chain so injured was condemned, on the vessel's being paid off at Portsmouth, and is now in the sail-field of the dock-yard, and I should think a link of it would be worth preserving in the museums of the different scientific bodies*.

"That the phenomena of earthquakes are produced by volcanic explosions, there can be little doubt, and that they are frequently accompanied by powerful electric action, has long been known. To which of these causes are we to look for the powerful effects here described?"

LXXVII. Observations on the Paddle-Wheels now used in propelling Steam Vessels, and on those recently invented and patented by JACOB PERKINS, Esq. Engineer.

SINCE the application of steam to the purposes of navigation, no description of machinery, except the steam-engine itself, has occupied so generally the time and attention of mechanics as the paddle-wheel. Inventions, endless in variety, have been patented for propelling steam-vessels : till lately, however, none have been found so efficient, durable, and economical, as the common wheel, notwithstanding its waste of power is very considerable.

When the dip of the common wheel is not more than one-tenth of its diameter, the waste is erroneously supposed to be inconsiderable; but when it exceeds that proportion, the loss of power is confessedly in geometrical progression, it being found that if the wheel be immersed to half its diameter, the strain on the engine becomes so

very singular effect, as described

* Our readers will find a notice of this to us by a friend who saw it at Portsmouth, in vol. V. page 272.-EDITOR.

great as to leave very little of its force applicable to the propulsion of the boat.

Of course sea-going steamers are, from the irregularity of the ocean's surface, more exposed to this injurious influence than vessels navigating rivers or quiet waters, where the dip of the wheel can be regulated.

It is obvious that the common paddle, when at the lowest dip, where it should have the greatest power, moves in water already disturbed by the preceding paddle, and it is evident that after the paddle has passed the lowest dip, it is not promoting the progress of the vessel, as it would do if it were acting in undisturbed water.

To obviate some of the difficulties above stated, an eminent individual, Mr. Oldham, of Dublin, has, in common with many others, taken great pains and incurred considerable expense. He constructed a wheel, the paddles of which enter the water edgeways, and by machinery attached to them, gradually change their position, until, on their successively arriving at the lowest extremity of the wheel's rotation, they present a face at right angles with the keel, and then gradually revolving, leave the water edgeways. But the complexity, increased friction, liability to derangement, weight and expense of this wheel, were found more than to counterbalance its theoretical superiority.

Simplicity, durability, lightness, and cheapness, are requisites not to be dispensed with in the construction of paddle-wheels. If with these essentials a wheel can be constructed to work with undiminished action, at a dip ordinarily of one-third, and occasionally of one-half its diameter, without incurring a greater consumption of steam power than attends the common wheel, when used in still waters, then a remedy will be found for the great loss now experienced in sea-going vessels. Such a wheel has lately been invented by Mr. Jacob Perkins.

Those who have witnessed the Chinese method of sculling, must be strongly impressed with the superiority of

that over the European application of the oar.

The action of Mr. Perkins's wheel is not unlike that of the Chinese scull; in fact, the only difference is, that the motion of the scull is reciprocating, that of the paddle-wheel in question rotatory; the rotatory motion being clearly preferable, inasmuch as the frequent change of motion in the scull is so much waste of power.

Comparative experiments with the common, and with the newly invented, wheel, alternately used in the same boat, have shown, that even at a shallow dip, the most appropriate to the common wheel, there is a very important gain with the wheel of Perkins. But when the wheels are each of them immersed to one-third of their diameter (perhaps an average dip for sea-going vessels), the advantage attending this newly invented wheel is scarcely credible!

Facts are stubborn things, opposed as they may be to the theories of men of acknowledged ability. It has been asserted by certain eminent engineers, that the common wheel admits of but little improvement. If it cannot be demonstrated that much power is lost by the common wheel, then would those engineers be borne out in their assertion. But recent experiments, made in England and America, prove the loss of power with the common wheel to be very much greater than had hitherto been imagined. If the loss were trifling, could a single horse on a towingpath do the work of a six-horse engine in the boat? Could two horses attached to the hawser of a boat, moved by a twenty-five horse power engine, neutralize the power of the engine, stay the progress of the boat, and occasionally give her stern away? These facts, however, are well

authenticated!

Engineers, who believe in the perfection of propelling machinery on the old plan, exultingly reply to these facts, by making abstract inquiries, such as, whether a vessel can move as fast as the periphery of the wheel by which she is propelled? Whether, if a boat move four-fifths as

fast as the periphery of the wheel, it is not considered fair speed? and then come to the conclusion, that the whole loss of power cannot exceed one-fifth, and that allowing for friction, it is absurd to expect to save much of that small proportion by any improvement. That this conclusion is premature, the following remarks are intended to prove.

Let it be supposed that a paddle wheel can be made of such power, and to have such hold on the water as to move only one-hundredth part faster at its periphery than the vessel it propels, the difference in such case between the relative velocity of the wheel and the vessel, would be as ninety-nine to one hundred. It is true the magnitude of the wheel would require steam power in proportion, and then the remedy would be as bad as the disease, but the case is practicable. To suppose, therefore, that the loss of power is only as the relative movement of the wheel and of the boat, is as absurd as it would be to assert, that inasmuch as the carriage wheel and its body move with equal velocity, it matters not what load the carriage contains. In the one case the speed or draught of the horses must be increased, so in the other must the steam power.

We will consider the subject, however, in a more tangible shape. There are four kinds of water-wheels, of which the undershot assimilates more to the paddle-wheel than the others; and the undershot wheel, it is acknowledged, loses two-thirds of its power, that is to say, if three pounds of water fall one foot on an undershot wheel, it will not communicate impetus sufficient to raise more than one pound to the height of the fall. Let us examine these data in three points of view with relation to the paddle-wheel.

1st. The undershot wheel is propelled by water descending on it.

2ndly. The water so falling is so directed as to strike the float-boards at right angles with their surface.

3dly. Although the power is communicated by water