1842.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



135 



ber in point of speed, he referred to the qualification of durability, which, he 

 said, involved a chemical question. Upon this subject he had been favoured 

 by Mr. R. Mallett, of Dublin, who had been employed in making experiments 

 for the British Association on the coirosion of cast and wrought iron, with a 

 short paper on the corrosion or fouling of iron ships, which was of great 

 interest, and would be published with the report of the lecture. He then 

 referred to the quaUtication of durability, and said, that in removing the 

 timber work of the ship John Garrow the dry rot was found. All the tim- 

 ber not exposed to the air had been affected by it, while that exposed to the 

 air was perfectly free from corrosion. The lecturer here exhibited an iron 

 bolt which had been taken out of the John Garrow. The part of it which 

 had been in oak was very much corroded, while the remaining part of it 

 vfhich bad been in iron was very little decayed. He was of opinion that 

 oxidation took place no faster on the surface of thick plates than on tliin 

 ones, and he did not believe that the thickness of wood had any effect on 

 its durability, so far as decay was concerned. The wear and tear of iron 

 vessels were trifling, while the expense of their repairs was hght. In a tim- 

 ber vessel, the expense of repairs would, in the course of ten years, equal the 

 first cost. In the case of an iron vessel no repairs would, in all probability, 

 be required within the first ten years. The expense of keeping the copper 

 of a timber ship in repair would amount to a sum equal to that of making the 

 whole of the repairs required by an iron vessel. 



The first cost was the next point for consideration. He wished ship- 

 owners to recollect that if they wanted good work they should give a propor- 

 tionate price, and he hoped in future that they would obtain good work, and 

 not be looking after a saving of expense. He had arrived at the following 

 conclusions, in order to convey some idea on the subject : — that good service- 

 able iron sailing vessels, of 300 tons, would be equal to timber ships of larger 

 tonnage ; that iron vessels had many advantages over timber ones ; that for 

 Tery large vessels iron would be less expensive than timber ; and that iron 

 vessels for rivers might be built at a less expense. He laid less stress on the 

 last qualification — that of light draught of water — than on others, but, at the 

 same time, a hght draught of water might be obtained in iron vessels. It 

 wonld be asked, therefore, why not have iron vessels more generally built, if 

 their superiority was so apparent ? He would not evade this inquiry, neither 

 would he forbear from alluding to the narrow poUcy of those who had 

 opposed the system. He admitted that there were some real objections which 

 had to be removed. Those objections had now, however, been set at rest. 

 The difficulty about the compass was one, and it was natural that the derange- 

 ment of the compass on board of iron vessels would have been a great obstacle ; 

 but this question had been entirely set at rest to all reasonable minds. Ship- 

 wrights and various other parties had also risen up against iron as a material 

 for ship-building ; everything was magnified, and it had been attempted to 

 put it down once and for ever. It was broadly stated tliat iron vessels would 

 never succeed ; and when an iron vessel arrived in the port on one occasion, 

 many went to look at her, and every possible fault was found with her. These 

 objections were now becoming weaker. He thought some blame was attri- 

 butable to the builders of iron vessels, and he called on builders not to place 

 the principle of iron vessels in jeopardy by constructing vessels which their 

 judgment might tell them would not be serviceable. Underwriters had not 

 been the last to find objection, for shipowners had been told that the pre- 

 miums would be very high on iron vessels, and that the subject had not been 

 sufficiently tested. The shells which adhered to the bottoms of iron vessels 

 had caused another objection to be raised. There would, however, be no 

 difficulty in removing the shells when first they adhered to the bottoms, if a 

 scraper were used, and this might be done by the sailors when they were at 

 liberty during the voyage. After explaining the manner in which the scraper 

 was to be used, he said that if the vessel were kept clean before she left the 

 port, and the scraper was used at sea, the shells would he removed, and an 

 iron vessel would be kept as clean as a timber one. 



The lecturer here expressed a hope that he had satisfied many doubts, and 

 awakened an interest in the breasts of some who never reflected on the 

 subject before. He instanced the fact that chain cables, steam navigation, 

 and many other inventions, had been met with opposition in the first instance 

 although in general use at present, and he prophesied tliat such would be the 

 case with reference to iron as a material for ship-building. He said he liad 

 a description before him of the " Great Britain" steam ship, but that the 

 lateness of the hour prevented him from entering into details. He then 

 referred to the facility which existed for altering iron ships, and said that 

 while the iron could be used again, the fact was otherwise in many cases with 

 respect to timber. He thought there could not be a belter period than the 

 present for considering a question of the present kind as a means for allevia- 



ting the general distress. If taken up as a national question it would be 

 attended with beneficial results. No one would deny that it was of impor- 

 tance that our ships should be constructed in our own ports, by men of our 

 own population, and with materials of our own soil, which materials were 

 obtainable in the deep recesses of the earth. The iron could be got at the 

 usual market price ; there would be an increased demand for labour ; and 

 few foreign timber ships could compete with Enghsh vessels, as all countries 

 yielded the palm to England in the use of iron. There appeared to him to 

 be only one obstacle to be removed— he alluded to national prejudice. The 

 Enghsh public were unwilling to give up their "old wooden walls." It 

 seemed as if they thought their glory wonld depart if they were to surrender 

 on this point ; but it should be remembered that the noblest specimens of 

 naval architecture possessed the seeds of decay, and that the royal heart of 

 oak would remain in the laud, if u-on were brought into general use. There 

 was one other result which the lecturer noticed, namely, that a 400-ton ship 

 would not produce £200 when condemned and broken up, while an iron 

 vessel, under similar circumstances, at is. per cwt., would produce 21. per 

 registered ton, or four times as much as a timber ship. 



He then concluded by saying that the present was the first time the subject 

 had been fairly before the public, and by hoping that he had advanced it 

 somewhat in the estimation of the meeting, and that in their progress, rise, 

 and end, wooden ships might yield to iron. The reading of the paper, which 

 occupied upwards of two hours, was received throughout with demonstra- 

 tions of applause and satisfaction. 



FROCEEQINGS OF SCIENTIFIC SOCIETIES. 



INSTITUTION OF CIVIL ENGINEERS. 



Jan. II. — The President in the Chair. 



" Description of a portion of the Works of the Ulster Canal." By Thomas 

 Casehourne, M. Inst. C. E. 



The Ulster Canal, which is described in this communication, was designed 

 for the purpose of facilitating the intercourse between the west and the 

 north of Ireland. It commences at the southern extremity of Lough Erne, 

 in the county of Fermanagh, whence it extends for a length of 46 miles, and 

 enters the river Blackwater, near the village of Charleraont, in the county of 

 Armagh, from which there is an outlet through Lough Neagh to the ports of 

 Newry and Belfast. The total cost of this work will amount to about 

 210,000?., or -ifidil. per mile. Allusion is made to a proposed junction 

 canal between the rivers Boyle and Shannon, which may be considered as an 

 extension of the Ulster Canal westward, effecting a junction between all the 

 navigations of Ireland. By its means the produce of the to%Tn of Boyle, and 

 the agricultural district around it, would be conveyed directly by steam to 

 Belfast and Newr)-. At the time of this communication, the Ulster Canal 

 was rapidly advancing towards completion ; it was navigable up to Clones, a 

 distance of 40 miles from its commencement, and would be opened to Lough 

 Erne during the summer of 1841. A description is given of the most diffi- 

 cult and expensive portion of the canal, which is situated at about six miles 

 along the line from Charlemont. The length of this part is about three- 

 fourths of a mile, and it comprises seven locks. The expense of construction, 

 exclusive of the value of land, was 17,053/. 4s. 9d. ; in order to diminish the 

 expense as much as possible, the canal was contracted in width in two points, 

 where the local impediments were considerable. The transverse dimensions 

 of the canal are, 19 ft. G in. at the bottom, 36 ft. at the surface of the water, 

 and 42 ft. at the top bank — giving a slope of 3 to 2 at the sides of the chan- 

 nel. The depth of water is 5 ft. 6 in. in all the reaches, except the summit 

 level, which is capable of containing 7 feet of water. The course of this 

 portion of the line lay along the bottom of a steep ravine in a Umestone rock, 

 parallel with the channel of a mill-race adjacent to the river Blackwater. 

 The mill-race was, therefore, diverted into the river between the first and 

 fifth locks of the canal. Between the third and fifth locks the bed of the 

 canal was formed by benching in the rock on one side, and embanking on 

 the other with the materials so obtained. Beyond this it was cut for a dis- 

 tance of nearly 350 yards through the limestone ; in one place to a depth of 

 41 feet. The sides and bed were there lined with puddle, and protected by 

 a facing of rubble wall. Thence, to the seventh lock, the channel was again 

 formed by benching and embanking through a clay soil, where much caution 

 was necessarily exercised in preventing sUps at the foot of the embankment, 

 which was sidiject to inundations from the Blackwater. The masonry was 

 all constructed of limestone from an adjacent quarry. Two appendices are 

 subjoined to this paper. The first of these gives in detail the items of ex- 

 penditure for the portion of the canal described ; the second contains a par- 

 ticular description of the locks and lock-gates, the bridges, and the earth- 

 work. The locks are 73 ft. long, 12 ft. wide, and vary in rise from 6 to 11 

 feet. They are all constructed in ashlar masonry, — The paper is accom- 



a* 



