GREAT MINING OPERATIONS NEAR DOVER. MAJOR-GENERAL SIR C. WILLIAM PASLEY has addressed to the Editor of The Times a long and important letter respecting the great Explosions near Dover, by which Round-down Cliff, an immense projecting mass of chalk in the proposed line of the South-Eastern Railway, has been thrown down. "To Mr. William Cubitt, the engineer in chief of the railway," observes the Major," is justly due the merit of having conceived the idea of removing a mass of chalk rock nearly 300 feet in length, but of still greater height, and averaging 70 feet in thickness, by simultaneous explosions of gunpowder, instead of employing labourers to scarp it away, which would, probably, have cost nearly £8,000; the merit of success also belongs to him, inasmuch as he took the most judicious means to insure it." Our further extracts relate to the firing of the batteries.

"The whole of the arrangements for firing these great charges by the voltaic battery were made by Lieutenant Hutchinson, assisted by Lance Corporal John Rae, and Private Thomas Smith, of the Royal Sappers and Miners, and by two naval pensioners, John Leary, a blacksmith, capable also of working in tin or copper, and William Gordon, a rigger, all of whom had been employed under the same officer at Spithead. Leary, who distinguished himself some years ago whilst under the command of Captain Dickenson, of the Royal Navy, by converting ships' tanks into a diving-bell, by means of which that enterprising and intelligent officer recovered the treasure sunk in the Thetis frigate on the coast of Brazil, was employed on his arrival at Dover in making voltaic batteries for the proposed explosions, nine in number, each consisting of six cells of Professor Daniell's constant battery, such as had been used by me in all my mining operations; and he also put together the wires for three conducting apparatuses, each 1,000 feet in length, and consequently composed of 6,000 feet of copper wire. Each apparatus consisted of a pair of wires attached to a strong rope, and secured and insulated by Gordon in the same substantial manner that had been adopted by us at Spithead; for though there was very little necessity for guarding against the action of water, yet the letting it down and dragging it up the high chalk cliffs exposed this apparatus to a good deal of wear and tear; and it might also have been injured by the hob-nailed shoes of railway labourers, to which it was continually exposed, as I observed particularly on the day it was used, when every person that came near it trod upon it; and which, had it not been thus protected, might have destroyed the connexion and prevented the explosion, of which I have known instances in the course of our former experiments. As soon as the batteries and conducting apparatuses were complete, Lieut. Hutchinson made experiments to ascertain whether he could fire all the three charges simultaneously by one powerful battery, as had been done by Dr. Hare, of Philadelphia, who first applied voltaic electricity to practical purposes, by using it for blasts in rocks to obtain stone for building, in 1831, as minutely described in Silliman's American Journal of Science, vol. xxvi. p. 352; and also briefly noticed in the Transac

tions of the British Association for the Advancement of Science, held in Bristol in 1836. From his own experiments, made with this object, Lieutenant Hutchinson drew the same inference that I had done about three years before,-namely, that one cannot depend upon more than two charges exploding simultaneously, for though by a battery of extraordinary power he succeeded in firing twelve small experimental charges at the distance proposed for the great mines under his direction, yet there was a perceptible interval of time between the reports, which resembled a volley of musketry rather than the discharge of a single gun. He therefore determined to adopt the plan which I had proposed to use in 1839, had it proved advisable to fire four subaqueous charges simultaneously against the wreck of the Royal George, namely, to have a separate voltaic battery for every charge, and a person at each, with one conducting wire fixed to the pole of the battery, and the other in his hand ready to complete the circuit, according to the time marked by the chief, who was to give the words one-twothree-with an interval of about one second between each, and then the word fire, which was to be the signal for completing the circuit; and by this mode I expected that the explosions would all take place simultaneously, on the principle of marking time in music. The powder in each of the three chambers prepared for the several mines at Dover was contained in bags, placed in a large box, the former expedient having first been adopted in the practice of the Royal Engineers at Chatham; but we never used box and bags also, which I considered superfluous. As these boxes formed what may be called double cubes, Lieutenant Hutchinson very judiciously had a couple of short branches forking out from the lower extremity of each conducting apparatus into two central points of the oblong charge. Very short and fine pieces of platina wire were placed, according to custom, near the closed ends of strong tin tubes fixed to the outside, and leading into the centre of the powder-boxes, in which tubes bursting charges of fine powder were introduced, surrounding the platina wires, on the same principle that had been used at Spithead, but without those extreme precautions that had been found necessary to resist the great pressure of water to which our charges there were subject.

"In the course of Lieut. Hutchinson's experiments, an unforeseen difficulty occurred, owing to Daniell's batteries, which had been very promising, losing their power after the first frosts set in. This difficulty had never embarrassed us before, because in our experiments at Chatham we always took the battery out of a warm room, and it required a longer time to impair its power than our experiments there ever occupied; and at Spithead, where Lieutenant Hutchinson first used the battery, it was generally kept in the cabin of one of our lighters; besides which the work was only carried on during the summer months. He was, therefore, obliged to have a small wooden shed built for his batteries at Dover, and to keep fires lighted whilst using them, by which he god rid of the difficulty.

"I have since been informed, that in experiments tried at Calcutta, a very energetic battery lost half its power when the temperature fell

from 120° to 60' of Fahr. When this difficulty occurred, a prejudice was naturally excited against Daniell's battery, and four very powerful plate batteries were ordered at Dover in consequence, which were made by an intelligent tradesman of that town. The trough of each of these contained twenty cells, according to Dr. Wollaston's construction, with zinc and copper plates, measuring seven by ten inches, the latter of which only were let down into the trough when the battery was about to be used; and these plate batteries were combined with the batteries made by Leary, as before mentioned; so that one wery powerful battery, consisting of forty plates of the common system, and of eighteen cells of Daniell's constant battery, was to be used for each of the three great charges.

"At the same time, I am now of opinion that the plate battery is the most convenient of the two for firing gunpowder, and the simplest that I have seen is that which is now being used by Mr. R. Davidson, of Aberdeen, in his interesting exhibition of electro-magnetic power at the Egyptian Hall, Piccadilly. This battery, which contains twenty cells, differs from Dr. Wollaston's in using amalgamated zinc, and in substituting plates of iron instead of copper, all the plates measuring eight by eleven inches, and the action being produced by diluted sulphuric acid, upon the purity of which, Mr. Davidson says, the efficiency of his battery chiefly depends. On inquiring who first adopted iron plates instead of copper, Mr. Davidson assured me that he had used the former metal himself for about twenty years, but that the merit of this arrangement was disputed by Mr. Sturgeon and Mr. J. Martyn Roberts. I advise those who ascribe the merit of applying the voltaic battery to the purposes of blasting in earth or rock, or the peculiar construction and management of the first plate battery, well calculated for this purpose, to any of our own countrymen, to refer to the documents before quoted, and they will find that they are doing an injustice to Dr. Hare, of Philadelphia. But it must not be forgotten, that Mr. William Snow Harris, of Plymouth, was prior even to Dr. Hare; having fired gunpowder by electricity in March, 1823, which he effected to the astonishment of numerous spectators by a common electrical machine, from the cabin of a small vessel at anchor in that port; whilst the charge was placed in another at a considerable distance, and separated from the former by the water, through which his conducting apparatus passed. But the electrical machine, though perfectly efficient, never would have superseded the common modes of firing mines, as the voltaic battery has done; because the former not only requires a much more delicate manipulation than could be expected either from civil or military miners, and would be more easily broken or deranged; but it also requires artificial heat at all times, even in summer; whereas the voltaic battery can always dispense with this very inconvenient arrangement, even in the depth of winter, excepting in the case of very long exposure to a low temperature."

A very minute account of this stupendous work, with nine clever engravings, will be found in the Illustrated London News, No. 40. On April 18, another of these extensive "blowings-up" of Dover

cliffs came off at Lydden-Spout coast-guard station. This blast proved proportionally successful in its effects to the unparalleled one, when, with the enormous quantity of 18,500lbs. of gunpowder, the destruction of Round-down cliff was effected on the 26th of January last. The mass of chalk operated on now formed the base of the same cliff, the crown of which, to the depth of 90 feet, was blown off by a blast consisting of 7,000lbs. of gunpowder, on the 2d. ult. The present blast consisted of upwards of 10,000 lbs. of gunpowder, which was placed in fifteen cells or chambers, at proper distances along the base of the chalky cliff about to be removed; and, the conducting wires being properly placed, all were fired at once, as on the occasion of the last blast, by an apparatus invented by the junior engineer, Mr. Hodges. This explosion seems to have created quite as great a sensation as the blast of Round-down.

NEW IRON BEACON FOR THE GOODWIN SANDS.

THIS Beacon, which has cost the inventor, Capt. Bullock, no little pains and expense to mature, is "ponderous footed;" and it consists of a cast iron chamber, six feet six inches high, by four feet square, terminating in a solid point, and weighing about four tons. Within the chamber there is contained a socket, which is strengthened by iron brackets. In this socket is fixed five feet of the circular shaft of the beacon, which is made of inch-iron, cast hollow, the diameter of the lower part of the shaft being seven inches, and of the upper six. The two portions of the beacon are united by a flange and core; and the entire height, from the top of the chamber to the mark, is twentyseven feet. The mark is an ellipse, six feet by four in diameter, composed of round bars of wrought inch-iron, strongly secured to the shaft by a flange and core, constructed so as to form a most conspicuous beacon, and also to offer the least possible resistance to the action of the wind. Next spring, by the direction of the Elder Brethren of the Hon. Trinity Board, it will be planted at the eastern end of the dangerous Goodwin, on the south side of the Swatchway into Trinity-bay. The sand at this part of the Goodwin is of a very hard and compact nature, so as to render the sinking to any depth a task of no very easy completion; but it is expected that the ponderous foot, or base of the beacon, being inserted some nine feet in the sand, the pressure from without of the sand upon the sides and the top of the base, in addition to its own weight (which when filled with sand, will be upwards of six tons) will secure its perpendicular position and stability.-Dover Chronicle.

MAJOR PARLBY'S BREAKWATER.

THE Society of Arts have voted to Major Parlby a silver medal, for his plan of forming Breakwaters, of which the following description has appeared in the Mechanics' Magazine, No. 1039.

The principle of this breakwater is taken from what may be observed in every part of the world-viz., the effects of reeds in rivers and lakes, and of seaweed in the ocean, in calming or subduing the

turbulence of the swell or waves. Now there is a fucus, or marine plant, common in the seas about the Cape of Good Hope, which grows in a long tubular form, from twenty to thirty feet in length; at one end-that which floats upon the surface of the sea-it has a trumpet-formed termination, while the other attaches itself to rocks at the bottom of the sea. This has served as a kind of model to Major Parlby for the construction of the component parts of his breakwater, which is, indeed, merely planting a complete bank of artificial gigantic reeds in the middle of the sea. Major Parlby's first idea was the employment of a considerable number of spars, such as those used for scaffolding, enlarging one end, and adding cork to make them more buoyant, and attaching the other end by a piece of chain or rope, to the bottom of the sea, by means of ballast, cast iron framings, or other practical means, and placing these spars about three feet from each other from centre to centre, and from fifty to eighty in depth; but an intelligent gentleman having suggested the employment of Indian rubber, Major Parlby purposes now to form the breakwater by pieces of the coir rope of India, (which is itself exceedingly buoyant, and almost imperishable in salt water), and coating and forming the reeds, or floating trumpets, with India rubber, so as, in some degree, to resemble the very weed itself. A more happy, or a more practical plan of forming a breakwater, can hardly be conceived, as they can be of every form, shape, and size, and have this peculiar advantage over all breakwaters that have yet been proposed, that they do not interfere with the sea way, but a vessel can sail through them without injury in every direction, and thus no particular entrance to a harbour is required, but vessels can enter whatever the wind and tide may be. The application of this breakwater (Major Parlby remarks) may be found of great service for the following purposes :-For protecting roads for shipping, barbours, piers, landing places, &c. For forming harbours of refuge in the open sea for ships, coasters, and fishingboats, wherever it is desirable, where good anchoring ground can be found. For preserving the coasts of the sea, and thus much valuable property from annual dilapidation and loss, by the falling of cliffs, the washing away of land, and from the effects of the violence of the waves. For breaking and calming the sea on all the sloping sandy shores where bathing machines are in use, so as to prevent the dangerous and injurious effects of breakers on the shore.

Practical men, who will immediately begin to inquire into the cost of breakwaters of this description, may be guided in their estimate by the calculation of the number of floating reeds, or trumpets required, placed at three feet apart, and fifty feet in breadth; a breakwater of extent equal to that at Plymouth, which is about 1700 yards, or nearly a mile, will require 1700+50=85,000; the cost of these will, of course, depend upon the depth of the sea, as the trumpets must be long enough to reach from the bottom to the top of the water at the highest tide; and, as far as calculations have at present been made, the expense of the coir and India rubber trumpets, with the cast iron gratings and ballast to fix them securely at the bottom of the sea, may