J 843.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



355 



of the observed sets, together with the calculated ones, from equal additions 

 of weight, from 56 to 4481b., derived from 44 kinds of cast iron, and from 

 90 to 100 experiments, were as follows : — 



Weights .. 56 112 168 224 280 336 392 448 



Mean sets .. -003 -013 -026 -047 -069 -102 -136 -197 



Computed sets parabolic -003 -012 -027 -047 -072 -102 -138 -181 

 Mr. Hodgkinson made experiments on stone, timber and wrought iron, and 

 observed the quantity of set in all. These different materials, when the re- 

 sults from them were constructed, all gave the form of the parabola, though 

 less perfectly than in cast iron, as the experiments on them were but few. 

 It appears, from the above-stated experiments, and others that were made, 

 that the sets produced in bodies, are as the squares of the weights applied. 

 Hence, there is no weight, however small, that will not produce a set and 

 permanent change in a body ; all bodies, when bent, have the arrangement 

 of their particles altered to the centre; and when bodies, as the axles of 

 railway carriages, are alternately bent, first one way and then the opposite, 

 at every revolution, we may expect that a total change in the arrangement 

 of their particles will ensue. It appears, too, from the results of these ex- 

 periments, that all calculations hitherto made, on the strength and elasticity 

 of bodies, have been only approximations. Mr. Hodgkinson stated, that he 

 laid the results of this communication before a meeting of the Literary and 

 Philosophical Society of Manchester a short time ago, soon after he had 

 made the discovery which it contains. In the prosecution of the experi- 

 ments he had received every assistance which the works of his friend, Mr. 

 Fairbairn, could supply ; and Mr. Robert Rawson had kindly assisted him in 

 the reduction and arrangement of the results of the experiments. 



This communication gave rise to much conversation, in which the Presi- 

 dent, Prof. Lloyd, Dr. Robinson, and other persons joined, and in which all 

 agreed, that these experimental inquiries were of the utmost importance in 

 supplying a solid foundation for the speculations of the mathematical inves- 

 tigator in this most difficult branch of physical inquiry. Dr. Robinson also 

 inquired, if Mr. Hodgkinson had observed whether the molecular structure of 

 the bodies, on which he had experimented, was altered in any manner, and 

 if so, how did the change take place, during the progress of the experiments ? 

 Mr. Hodgkinson replied, that he had no means of determining this point 

 satisfactorily, but he had no doubt, that matter, when subjected to strain, 

 long before it broke, had its molecular structure permanently deranged. 

 He exemplified this by the axles of locomotive engines, which, as they 

 turned round, had the parts that were extended and compressed successively 

 underneath and above ; and after this action had been continued for a long 

 period, they were found to become of a kind of crystalline structure, inter- 

 nally, and of course were much impaired in strength. — Prof. Stevelly said, 

 that the forces to which they were subjected were in kind, though not in 

 degree, something like the alternate bending back and forward of a piece of 

 wire under which it at length broke. — Mr. Hodgkinson assented. 



" On Changes in the Internal Construction of Metals." 



Mr. Lucas, in the absence of Mr. Fairbairn, reported the progress of the 

 Committee appointed at the last meeting, to ascertain experimentally whether 

 any and what changes take place in the internal constitution of metals ex- 

 posed to continual vibration and concusssion. (The results of these expe- 

 riments were stated by Mr. Hodgkinson in the last paper). — The effect of 

 concussion on the shafts of tilt hammers is very remarkable. The shaft- are 

 made of the best ash, but after three or four months' use the strength of the 

 wood is so much deteriorated that the shafts break off short as if they were 

 rotten. Copper is also similarly affected by concussion, and in working 

 copper articles, and in rolling silvered plates of copper, the workmen find it 

 necessary to anneal the metal to prevent it from breaking..— Mr. J. Taylor 

 observed that this subject had been much discussed at Manchester, and with 

 the same results. He alluded to the difficulty of procuring good chains, and 

 said it occurred to him that probably it might arise fronTthe chain maker 

 being too good a workman, and that the evil was caused by too much swaging 

 in finishing the work. If, however, the quality of the iron could be restored 

 by annealing, as might be inferred from these experiments, that would pre- 

 sent the means of obtaining good chains in the first instance and of strength- 

 ening them after use. 



On Contoured Maps, by Captain Larcom. 

 It is important that maps constructed by the government should exhibit 

 the levels of the country in the most intelligible manner ; showing heights 

 not uierely on the tops of hills, but round their sides, and through the valleys 

 which traverse them. Such a system is offered by these contours. They 

 are a series of horizontal lines, at a certain distance asunder, and at a certain 

 height above a fixed datum. The datum most commonly used is the level of 

 the sea, doubtless from the shore line being the limit of the land, and the 

 point at which roads must cease, as well as from an impression that it is 

 itself a level line ; and therefore, as the first contour, the most appropriate 

 and natural zero, from which to reckon the others. The Section were aware 

 that it has been a point much discussed, whether the high water, the low 

 water, or the mean state of the tide, offers the most level line. This is a 

 point which it would be out of place to discuss here, but it may be stated 

 that, in order to determine it, as far as Ireland is concerned, a series of lines 



has been very accurately levelled across the island in various directions, and 

 permanent marks are left in all the towns, and on numerous public buildings ; 

 and at the end of each of these lines on the coast, tidal observations have 

 been made every five minutes during two complete lunations. These obser- 

 vations, and the connecting lines of level, are now in process of reduction — 

 the degree of accuracy attained is such that a discrepancy of - 2 of an inch is 

 immediately apparent — and from them we may expect many points of in- 

 terest. The steeper the natural slope of the ground is, the closer together 

 the contours, of course, will he, aud the more oblique the road ; where, on 

 the contrary, the ground slopes very gently, the contours are further asunder, 

 and the road may he proportionally more direct. By examining the maps of 

 the Irish Survey, on which contours have been drawn, it will be seen that 

 they tell sad tales of the existing roads, every one of which ascends and 

 descends frequently, instead of keeping ou a gradual slope for its whole 

 length. In order to exhibit these lines, it is proposed, instead of adding 

 them to the original copperplate, which has a peculiar value as an official 

 record of boundaries, to make a copy of the plate by the electrotype, for the 

 purpose of receiving these lines. Contour maps were thought of early in the 

 progress of the survey, but means were wanting for their execution; at pre- 

 sent, however, the outline survey being complete, and the general map, or 

 map of the surface, being in progress, affords a convenient opportunity, 

 which it is hoped will not be lost. 



Dr. Robinson inquired of Capt. Larcom whether the process of contouring 

 the maps was proceeding, and how soon he supposed it would be completed 

 for Ireland. — Capt. Larcom replied, that for the present it had been sus- 

 pended. — Dr. Robinson observed, that whether he considered the value of 

 this process in relation to the general interests of science, or the most im- 

 portant practical economies of the country at large, he could not but deeply 

 deplore the suspension, temporary though he hoped it would be, of this great 

 national undertaking ; and he trusted that, before the British Association 

 closed its present sitting, the most energetic steps would be taken to make 

 such an application to government as would induce them to resume this 

 most valuable work. He begged to inquire from Capt. Larcom, what 

 the expense would probably be. — Capt. Larcom replied, that he should esti- 

 mate it certainly at less than a farthing an acre. — Dr. Robinson : And the 

 original cost was probably sixpence or cightpence. — Capt. Larcom 6aid, 

 perhaps sevenpence to ninepence. — Dr. Robinson : Then, at a cost of about 

 one thirty-second part of the original expense, this invaluable additiou to that 

 splendid work, the Trigonometrical Survey of Ireland, could be accomplished. 

 If it was determined finally to suspend this work, he should say that it was 

 very like what the homely adage characterized as penny wise and pound 

 foolish. 



" On a Method of ascertaining Inaccessible Distances at Sea or Land." 



Mr. P. Leahy read a paper on a method of ascertaining inaccessible dis- 

 tances at sea or land, for which he claimed the advantages of greater accu- 

 racy and expedition than by the method of measuring a base line by the 

 log. On his plan two small telescopes are fixed at the greatest distance the 

 vessel will admit of, and so as to form some multiple of ten feet. This dis- 

 tance forms the base line on which the calculations are to be made. — Mr. 

 Macneili. being requested by Dr. Scoresby to state his opinion of the in- 

 vention, the latter said that it was sound in principle, but he thought with so 

 short a base line aud with the difficulty of taking simultaneous observations 

 at sea, it would be liable to inaccuracy. 



" Formation of Concrete." 



Mr. Hawkins made a communication on the formation of Concrete, 

 showing more particularly the importance of having the stones of the proper 

 sizes, so that the smaller ones should as nearly as possible fill up the inter- 

 stices of the larger. Where the sizes were properly adjusted, he found that 

 one proportion of lime to twenty of shingle, formed a stronger concrete than 

 when larger proportions of lime were used. Some engineers are in the habit 

 of using one of lime to six of shingle, and the proportions generally used are 

 as one to eight. A specimen of concrete made in the proportions he recom- 

 mended, and with shingles of proper sizes was found after a short time to be 

 stronger than an old Roman wall. — Mr. Macneili. said he preferred artificial 

 cement to lime, and he had found great advantage to result from allowing 

 the mass of concrete to fall from a height, by which means the shingle be- 

 came more compressed together. Mine dust mixed with lime, he believed, 

 made the most perfect concrete. — Mr. Jessop and Mr. Taylor also approved 

 of mine dust. The latter observed, that it was probably from the quantity 

 of iron in mine dust, that its adhesive properties were derived. 



" Raising Sunken Vessels." 



Sir T. Deane explained the method adopted by his brother. Mr. A. 

 Deane, to raise the Innisfaile steam vessel, of 500 tons, which was sunk by 

 striking against an anchor in the Cork river a few years ago. The ordinary 

 methods of raising sunken ships having proved ineffectual, a coffer-dam was 

 made round the vessel in the middle of the river ; and pumped dry by means 

 of eight or nine chain pumps. The leak was ascertained by digging under 

 the ship, and a cow hide was nailed over it to keep it water-tight. The 

 coffer-dam was removed as quickly as possible, when the Innisfaile again 

 floated by her own buoyancy, and the steam having been got up, she was 

 taken to Passage to undergo the necessary repairs. The whole cost was 

 400?., and the work was done in the course of four tides. 



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