This solid divided by 35, the number of cubic feet in a ton of water, will give the tonnage or weight of the lading; and as the tonnage, to be correctly reckoned, should be the measure of the number of tons of the lading of a ship, that weight which brings her down from the lightwater to the water line cannot fail in being correct.

Another difference which is observable between the ships of the British and those of the French and American navies, is in the height of the masts they carry, particularly in the mercantile shipping, which, with the defects in the formation of their hulls, in general renders them worse sailers than those of either of the above nations. We here give the height of the masts, &c. of a 74-gun ship of our service, from Edye's naval calculations :—

to which are to be added the top-gallant-yard royal masts, the heights of which are uncertain.

We have endeavoured to show that the rules by which the tonnage of our ships is reckoned, is one of the principal causes why the mercantile navy of our country is in general, both in its appearance and in its qualifications, so much inferior to the American as well as the naval powers of Europe. Captain Marryat says, "that from this and other causes our merchant vessels have lost their sailing properties." He states that the American ships are the fastest sailers in the world, and that though they are at a much greater expense in their equipment, yet that they can afford to take freight at a lower rate; that they give higher wages and outbid us, and get all our best seamen. Their ships, he says, sail so fast, that they can make three voyages while our vessels can make but two; and that being better manned, and giving the quickest return to their employers, they are always preferred. There is no doubt that fast-sailing ships can always afford to be better manned, and that though the cost of their outfits is greater, yet the greater certainty of their arriving at their destinations, especially in long voyages, in a given time, must amply repay the extra expense.

There remain to be considered many improvements in naval architecture which should be applied to our merchant ships, especially the principle on which they are constructed, and more particularly as regards the putting together their ribs or frames. At present, in the arrangement of the materials, the practice is, that in forming the frames or ribs, half of the timbers are so united as to constitute only part of an arch, the alternate ones being only connected together, and the intermediate timbers called felleys being unconnected with each other, and only resting on the outer planking instead of giving, as they ought to do, support to it: so

constructed, they do not possess near the strength they would if the whole were formed into frames or arches.

The limits of a notice of this nature will not allow of space sufficient to point out many defects which are to be found in the general construction of the British mercantile marine, and which, in their consequences, have generally rendered it inferior to that of the Americans. We think that it can hardly be denied, whatever other causes may be in operation, that the principal is the mistaken and unscientific way by which the admeasurements of tonnage are taken; and it is to be hoped and expected, as it is the duty and the interest of the government and revenue, and also really that of the merchant himself, that the true and just estimate of the tonnage of his ship should be made, the more especially at a time when we have such daring rivals on the seas, that a subject of such importance will not be long before it is inquired into and amended. P. H. R.

ADMIRAL BULLEN'S PLAN FOR THE PREVENTION OF ACCIDENTS IN ASCENDING AND DESCENDING PITS.

THE fatal accident at Radstock Coal Pits, where twelve men lost their lives by the breaking of a rope at the pit's mouth, will be fresh in the memory of our readers. Admiral Bullen, of Bath, has transmitted us an account of a plan which he has invented for the purpose of preventing similar mischances. We readily publish it, in the hope. that those most concerned will see the absolute necessity of adopting every precaution against accident, where men peril their lives in undertakings for the benefit of their fellow-creatures. The worthy Admiral's plan is as follows:

Instead of one rope, by which the men descend and ascend the pit, I would recommend two, both of equal size and strength; one I would call the working-rope, to which the hooks and other contrivances are fixed, for the men to sit on in their descent and ascent-the other rope I would call the safety-rope, and to which should be attached a net bag, made of suitable strong rope and large meshes; this bag should envelope the men as they sit on the hooks, and are suspended by the working-rope. Now, should the working-rope break, the men would be received into the net, and saved from being precipitated down the shaft. These ropes should be tied together at proper distances that they may both work parallel in the groove of the large sheave or roller, that is fixed over the pit's mouth. Whether the ropes (if flat) will be better arranged by being placed over one another, or side by side, I leave to the judgment of those who superintend the machinery at the pit. The safety-rope may be used for years, as there is no strain and little chafing on it; but the working-rope becomes weaker daily, and at last separates, with destruction of human life or fracture of limbs.

JOSEPH BULLEN.

DEEPENING THE BEDS OF NAVIGABLE RIVERS.

THE entrances or mouths of all rivers, it is well known, are in a constant state of decay the water in them is every day, and every hour, decreasing in depth. The alluvial matter, varying in quantity, according to the different soils through which a river flows, is deposited at its mouth, and there accumulates to such an extent as to form a bar, which at last becomes impassable. The consequence of this natural and unceasing process of decay has been, that many proud and magnificent ports have, in remote periods, existed and flourished, of which perhaps there is now hardly even a trace.

The application of steam, however, to the purposes of navigation has, in our day, happily opened a new era in regard to the debouchures of navigable rivers. Steam has (amongst other important advantages) enabled us, by means no less simple than effective, to counteract, in a great measure, the unceasing operations of nature.

No further back than the autumn of 1837, Captain Denham, Marine Surveyor of the Port of Liverpool, reported to the British Association that "the river Mersey was shoaling up so fast that, if no means were soon adopted to avert it, the time was not far distant when Liverpool would cease to be a port."

It must be unnecessary here to dwell on the great importance of Liverpool as a port, and the anxiety which the above but too well founded prognostication (according to the then existing circumstances) naturally produced. No city of England-nay, of Europe-has increased so rapidly in wealth and extent, within a short period, as Liverpool— chiefly arising from its favourable situation. The docks and warehouses in Liverpool surpass in size even those of London, and the town is daily extending.

It is material to observe, that had Capt. Denham, or the Corporation of Liverpool, known then what has since been suggested to them, it is quite evident that the above alarming prognostication would never have been promulgated.

On reading Capt. Denham's report, just quoted, to the British Association, Mr Tait, civil and military engineer, on the 24th of May, 1838, suggested to the Mayor and Corporation of Liverpool,-" to agitate the bed of the river Mersey, at those places requiring to be deepened, by means of HARROWS or RAKES, to be attached to steam-vessels or steamtugs, and to be dragged by them backwards and forwards during the ebbing tide only." He sent them at this time a rough sketch of his idea, and shortly afterwards he forwarded to them working drawings.

Mr Tait's plan has had the desired effect. Eleven feet of additional depth of water have been obtained by it. Below this depth it appears that the sand in the bed of the river is so coarse and heavy that they have now recourse to dredging it. They find that this heavy sand is no sooner agitated by the harrows or rakes than, like the fat boy in Pickwick, it resumes its original place and falls asleep again. Dredging is a very slow, expensive, and uncertain process. It has been tried on the Thames for many years, and, notwithstanding some hundred thousand tons of ballast have been raised annually, it was found that the water every year continued to decrease in depth.

At the last meeting of the British Association, held in Birmingham, Mr Yates reported "on the changes and improvements in the embouchure of the Mersey," as follows:-"Lately a diagonal channel has been formed

by aiding the ebb current of the tide in its natural diagonal course, between Lancashire and Cheshire. This was done by DREDGING by means of a double-toothed harrow, twelve feet across, dragged backwards and forwards, by a steamer of 100-horse power, over the intruding banks," &c. "An enormous wooden scraper is also used. The matter taken up appears to contain a small portion of peat, and weighs somewhat lighter than the sand found within the estuary. This new channel has been proved to answer the purposes of navigation beyond original expectation, and the approach to Liverpool is even better than before."

In the above report there is obviously, and no doubt unintentionally, a confusion of terms. "DREDGING by means of a double-pronged harrow" is far from being intelligible. Dredging and harrowing are well known to be two very distinct and separate operations. Harrowing is used for the purpose of disturbing and agitating the detritus, so as to enable the ebbing tide to carry it off; whereas dredging is an equally well known operation, by which buckets, attached to an endless chain, are let down into the bed of the river empty, and brought up, on the other side of the chain, loaded with stuff, which, at the summit of the chain, they empty into a lighter alongside of the dredging vessel. The use of "a double-pronged harrow” in the process of dredging, therefore, can hardly be surpassed by the very efficient project of helping one's self to soup by means of a double-pronged fork! Harrowing might have been employed in the Mersey, and dredging also might have been employed; but it does not therefore follow that they are one and the same operation. It is necessary to call attention to the above distinction.

Mr Yates is a member of the Dock Committee of Liverpool, and could not, of course, have any motive in misrepresenting the operations in the Mersey, which have so materially contributed to produce a result of such vital importance, not only as respects Liverpool, but as respects all ports similarly situated. It has, in fact, now become a national affair.

By the timely application of harrowing or raking, the port of Liverpool has thus been saved from impending and inevitable ruin. "The approach to Liverpool," Mr Yates says, "is even better than before." From the coarse nature of the sand at the depth of eleven feet, however, dredging may now perhaps be necessary; but until this depth was attained the dredging was only had recourse to merely to ascertain, from time to time, while the harrowing or raking was going on, the kind of stuff (peat, or sand, or mud) which, at certain depths, they were harrowing over. The harrowing was found to be the chief and most efficient agent during their operations. In recommending harrowing or raking by means of a steamer, Mr Tait, in his letter of the 24th of May, 1838, to the Mayor and Corporation of Liverpool, stated that his confidence in the plan he suggested arose from the circumstance of his having found that when the mooringchains in the mid-channel of Bridge Reach, in the Medway, were in a line with the stream, and rubbed on the ground, the river constantly preserved its depth, although, on both sides, the shoaling increased; and he added, that, in sending them his plans (in their emergency) thus freely and offhand, he relied most confidently on their good faith and honour. subject of deepening the beds of navigable rivers is one of vast importance, and to which the attention of our annual conservators of the Thames cannot too frequently be directed,

The

VOL. II.

K

AEROSTATION.

INQUIRY RESUMED.-PARTIAL DIRECTION OF THE BALLOON.-SURVEY OF UNKNOWN LANDS.-MILITARY OBSERVATIONS.-SCIENTIFIC EXPERIMENTS.

FROM what we have stated in our last, both of our own conclusions and the observations of Mr Charles Green, the reader may now form some estimate of the nature and prospects of that undertaking which our distinguished countryman, with ingenuity and boldness in the conception not more remarkable than the modesty he displays in the communication, has proposed to himself to accomplish. Not that we have the presumption to suppose that any statement we could make upon the subject, however clear or comprehensive, could suffice to determine, either one way or the other, the opinions of the public regarding the issue of so novel, and indeed it must be admitted so apparently precarious an adventure. With or without the aid of such feeble lights as we have been able to bestow, we are still content to believe the large majority of the world will ever continue to view the attempt with feelings of doubt and distrust, which nothing short of absolute demonstration will ever be able effectually to

remove.

This, however, is a state of things by no means unnatural or even uncommon. In the infancy of the greatest discoveries, an universal disinclination to credit their success, until evinced by actual experiment, has ever been observable; and long after their properties and powers had been practically determined, their applicability to purposes far inferior to what they have since been proved to be competent, will be found to have been ever most generally misdoubted and denied. When the original investigators of the elastic power of steam first ventured to declare their expectations that by its means a progress might be accomplished, and a command acquired over earth and sea to which all our previous efforts would appear but the feeble exertions of infancy, who did not deride their predictions as the vain speculations of an ardent and overweening imagination?

If this has been the case with arts dependant upon principles more easily reducible to practice, and involving only the elements with which long experience has made us intimate, it is not surprising it should be doubly so in a proceeding where all is new, and the medium of conveyance as much beyond our control as its laws are at present beyond our comprehension. Equally ignorant as we are of the causes which govern the direction of the winds, and dubious even whether, if we had such a knowledge, we could render it with certainty available to the purpose, the success of any scheme which is dependant upon their agency, may well be regarded with suspicion, even by those who are really capable of reasoning upon the matter; much more so by the great mass of mankind, whose ignorance, more than their knowledge, is the criterion by which they calculate and decide. Deprecating, therefore, all hasty conclusions upon the subject, we remit the consideration of its prospects entirely to the judgment of the reader; simply observing, that as the mere novelty of any undertaking is by no means an argument against its practicability, so neither should its magnitude in the eyes of the uninitiated be taken as conclusive against the opinions of those who have made the subject their peculiar study, and who, as in the present instance, have already estabfished their claims to deference and respect by the skill and judgment