382 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. [December, 



Extreme length 

 Between the bearings 

 Depth at centre 

 Width of bottom flanch 

 Thickness of ditto 

 Ditto of body of girder 

 Width of top flanch 

 Thickness of ditto 



Ft. In. Ft. in. 



60 80 8 



jo 73 

 2 34 18 



10 10 



3i 2f 



on 2 



6 3 7i 



2.J IJ 



Mr. Redman has subsequently communicated to the Secretary of the In- 

 stitution of Civil Engineers a letter from Mr. Fairbairn, in which he says, — 



" Since the receipt of your note of the 13th instant, I have gone into the 

 calculations of the strengths of the girders composing the Gravesend Terrace 

 Pier, and find tliem as under: — 



Breaking weight of the large bearers, 50 feet span . . 8I5 tons. 

 Breaking weight of the small hearers, 22 feet span . . 35 tons. 



" I have computed these weights, on the assumption, that I am correct in 

 the distances between the supports, and that the other parts of the section 

 are a proportional of tJie middle, which I find to be nearly the case. You 

 may therefore consider the whole perfectly secure if not luaded beyond 80 

 tons in the one case, and 30 tons in the other, equally distributed over the 

 surface or whole length of the bearers." 



IMPROVEMENT OF THE PAUMBAN CHANNEL. 



Between India and Ceylon. 



There is scarcely any more gratifying proof of the triumphs of modern 

 engineering and practical science than the facilities which have within 

 these few years attained in the communication between this country and 

 India. The engineering operations recently undertaken at the instance 

 of the Indian government, for widening and improving the passage be- 

 tween Ceylon and the main continent of ludia, form an important part of 

 the efibrls made for shortening the travelliug distance from England to 

 Calcutta and Madras. The following account of these operations is 

 taken from the " Foreign Quarterly Review." The effect produced gains 

 additional vmlue from the fact, that the voyage round Ceylon is almost 

 always delayed by strong opposing currents. The distance saved by 

 the improvement of the Paumban Channel is nearly 3,000 miles. 



Before the survey of the Chagos Archiepelago had been completed, the 

 government of Madras made an application to that of Bombay, for a sur- 

 veying party to examine the Gulf of Menaar. The idea of this under- 

 taking originated with (jeneral Monteilh, chief of the Madras engineers, 

 who, having been wrecked on the shores of this gulf in 1S09, had from 

 that time forward felt ihe strongest possible desire to see its coasts, and 

 shoals, and sunken rocks, examined and laid down, in order, as far as 

 possible, to diminish the obstructions to navigation. In consequence, 

 Lieutenant Powell was ordered to detach himself from Captain Moresby, 

 and with Lieutenant Elhersey under liis orders, to undertake this ser- 

 vice. At the same lime a party of Madras engineers was engaged, 

 under the direction of General, then Colonel Monteilh, in cutting a navi- 

 gable channel through two formidable ledges of rock, extending from the 

 island of Kamisseraiu to the coast of Madura, on the continent of India. 



The passage through these rocks, while they remained in their natural 

 state, had a depth of at most six or seven feet, while on the great horse- 

 shoe sand bank, a little to the south, there was scarcely a depth of five 

 feet at high water. Notwithstanding these obstacles, however, numerous 

 small craft enaaged in the coasting trade had long made use of the chan- 

 nel, though always compelled to land a portion of their cargoes on enter- 

 ing the strait. The object of the Madras government was to widen aud 

 deepen the passage, so as to obtain a sufficient depth of water for vessels 

 of moderate burthen, and for the steamers from the Red Sea to Calcutta, 

 when they should be established. 



In order fully to comprehend the value of the works projected by the 

 Madras government, certain facts, not perhaps gent-rally known, must be 

 borne in mind. Up to the year 1837, when General Monteilh commenced 

 his enterprise, all vessels beyond the smallest class were compelled, in 

 passing from one side of the Indian peninsula to the other, to beat round 

 the Island of Ceylon, sometimes in the teeth of heavy and contrary winds, 

 and always agajnst currents more or less powerful. The addition thus 

 made to their voyage consisted under the most favourable circumstances 

 of at least 2000 miles ; but as it was oflen necessary to run down ten de- 

 grees of latitude before they could open the Bay of Bengal, they had to 

 sail full 35l>0 miles ere they recovered their proper course. The craft 

 exposed to this inconvenience and loss of time were engaged in conveying 

 the produce of Malabar, Travancore, and other fertile provinces, to 

 Madras. 



It is easy to perceive how very materially such a state of things tended 

 to enhance prices on the coast of Coromandel. Fewer persons would en- 



gage in the trade because of Ihe dangers to he apprehended in rounding 

 Ceylon ; while the mere length of the voyage, by multiplying the wages 

 of crews, and the interest of capital, necessarily raised the prices of com- 

 modiiii'S. Its general eflect, however, was to confine the coasting trade 

 chiefly to small vessels, which by the slow and laborious process of light- 

 ening themselves, by landing a portion of their cargoes during the passage 

 of the Strait, and afterwards re-shipping it, could reach their point of 

 destination through the Gulf of Manaar and the Paumban passage. 



It is well known that the dangers and difficulties of the Faro of Mes- 

 sina have called forth on that point of Sicily Ihe energies of a hardy race 

 of pilots, who subsist by the inhospitable character of their coast. Some- 

 thing similar has taken place in the little island of Ramisseram, where the 

 village of Paumban owes existence to the intricacy and shallowness of 

 the neighbouring channel. Circumstances, it will readily be perceived, 

 may occur which would render the impractibility of this route a public 

 calamity. Of this, an occurrence which took place in 1839, may be re- 

 garded as a proof. The " Enterprise," a well-built and powerful steamer, 

 bound, with treasure and arms, for Sinde, during the war in Ati'ghanistan, 

 was completely beaten back and detained for weeks by the force of the 

 south-west monsoon, vihile numbers of coasting vessels were passing and 

 repassing daily through the Paumban Channel, completely under the 

 shelter of land. From the detention of the " Enterprise," no particular 

 evil, as it happened, arose ; but had the fate of India depended on her 

 progress, she could not have overcome the resistance of the weather. 



The attention of government was directed to this suhject as far back as 

 1828, when some eflbrts were made towards removing the principal ob- 

 stacles to the navigation of the Paumban passage. For reasons which 

 are not stated, these labours were discontinued, and not again resumed 

 till 1837. In Ihe February of that year, Colonel Monteilh sailed from 

 Madras with a party of sappers and about fitly convicts. His journal of 

 proceedings, though too voluminous for publication, is, from its very mi- 

 nuteness, highly interesting. He describes, with soldier-like simplicity, 

 the aspect of things at his arrival, which was sufficiently unpromising. 

 An immense congeries of rocks, many of them rising to the surface of the 

 waves, at high water, the small and venturous craft of Ihe country steered, 

 as we have seen, their tortuous, if not dangerous, course. Through the 

 politeness of General Monteilh, a section of the rock is now lying before 

 us, together with a plan of the canal through the reefs. 



The geological structure of the strait is curious. First, commencing at 

 the north, we have coral and limestone, to which succeeds shingle, mixed 

 with granite boulders, but not loose. Having passed these, we come upon 

 a breadth of blue soft sandstone, mixed with lime and madrepore. Then 

 follows the great northern reef, composed of hard red sandstone, and ex- 

 tending east and west almost in a right line. Having traversed this, we 

 reach a broad belt of broken sandstone, interspersed with boulders of 

 other substances, and then come upon the southern reef, consisting, like 

 the former, with which it runs parallel, of hard red sandstone. A bed of 

 the same rock, but less indurated, then stretches southwards to the site of 

 the great sand bank. 



It is not very surprising that persons taking only a cursory view of 

 this formidable mass of obstacles, should have pronounced it insurmount- 

 able, and been disposed to turn into ridicule the sanguine colonel of engi- 

 neers who was about to encounter Ihem. Nor ought we, perhaps, to 

 wonder that the Court of Directors at home should, at first, have put 

 little failh in the success of the enterprize, and felt no way disposed to 

 sink a large sum of money among the submerged sandstone, shingle, and 

 boulders, we have above described. But Colonel Monteilh was all along 

 perfectly confident. He maintained that, if the requisite means were 

 placed at his disposal, he could cut through the interposing reels a chan- 

 nel of fourteen feet at low, aud sixteen at high water, and at Ihe same time 

 of sufficient breadth to allow of its being safely navigated at all seasons. 

 He located his gangs of convicts on the Island of Ramisseram, where he 

 likewise erected barracks lor the troops. A large diving bell, five tons in 

 weight, was sent him from Ceylon : he purchased or constructed various 

 catamarans, and with the least possible delay commenced operations. 



Perhaps the most laborious work was removing the huge fragments of 

 rock when they had been detachsd. This was effected by raising and 

 swinging them to the sides of Ihe catamarans, or large boats, by which 

 they were carried away and dropped into the sea, with the view of form- 

 ing a sort of breakwater on either side of the channel. Sometimes the ex- 

 plosion under water took place beftire the men could get out of the way, 

 and on one occasion a large catamaran was overturned with six persons 

 upon it. Another time, when the fuse had been twenty two minutes 

 without exploding, a diver was sent down to withdraw the powder, but 

 found the fuse burning fiercely, and had scarcely eirected his escape 

 before immense fragments of rock were projected above water, and scat- 

 tered with tremendous force on all sides. 



During the whole period in which operations were carried on, however, 

 few casualties occurred, while the deaths from sickness were scarcely 

 greater than they would have been in any ordinary service. This must 

 have been chiefly owing to the excellent system of management pursued 

 by General Monteilh, who treated all those under his care with remark- 

 able humanity. At first, many unnecessary difficulties were added to 

 those offered hy the nature of the ground ; but these were at length re- 

 moved, aud a powerful steam-dredge was sent out from England, which 

 cleared away the loose rock at the rate of about 2000 cubit feet per day. 

 Nevertheless, the channel has not yet been excavated to the depth re- 



