1819."] 



THE CIVIL EKGINEER AND ARCHITECT'S JOURNAL. 



2C0 



many purposes ; but he believed that some of the rocks in the neiijbbourbood 

 of Dundee would furnish a preferable kind of stone for such works, because 

 the Dundee stone weighed from 25 lb. to 30 lb. per cubic font more than the 

 Craigleith stone, and it could be procured in blocks of much greater size at 

 the same cost. 



Mr J. R. M'Clean said that the Barrow and Piel sea embankments of 

 the Furness Railway, which were each about one mile in length, were some- 

 what peculiar in construction. The situation was generally well sheltered ; 

 but during the equinoctial gales, the banks were exposed to a heavy sea. 

 The embankments were formed of sand, faced with a thickness of 12 inches 

 of clay puddle, into which a thickness of about 4 inches of broken stone 

 was beaten, so as to form a clay concrete bed to receive the pitching, or 

 stone facing, which was 12 inches in depth. The portion of the embank- 

 ment above the level of the equinoctial tides, was faced on each side with 

 sods 6 inches in thickness, cut from the "salting." The grass, although on 

 a slope of one to one on the inner side, was very strong and luxuriant, and 

 the parapet thus forjned afforded a complete shelter for the railway. The 

 cost of the stone facing, including the puddle concrete, was Is. 6d. per 

 superficial yard, and that of the sodding was 3d. per superficial yard. This 

 form of embankment was, in his opinion, better adapted to the situation, 

 and was constructed at less cost than an upright wall would have been. He 

 agreed with the statement made by Mr. Green, that the greater the slope of 

 the face of the embankment, the less would be the disturbance to the fore- 

 shore; and he thought that the necessity for pitching and putting down 

 groynes to protect the foreshore, when an upright wall was built, proved, 

 in a great degree, the correctness of this principle ; more especially when 

 the foreshore was composed of alluvial deposit, or other matter of a light 

 description. 



The Rev. the Dean of Westminster, directed the attention of engineers 

 to the shape of the Cob Wall, which formed the extremity of the pier at 

 Lyme Regis, Dorset. It was a nearly vertical wall, with a rounded end, 

 built of Portland stone, and the stones were fastened together with oak 

 dowels ; it projected about a furlong into the sea, at a depth of 10 feet at 

 low water, and was exposed to all the force of the Atlantic ; but it was 

 placed at such an angle to the run of the sea that it appeared to divide the 

 waves, deflecting one portion innocuously past, to expend itself gradually 

 upon the beach, leaving still water within the port, and turning aside the 

 other portion in such a manner along the flank of the wall, that the body of 

 water might interpose between the masonry and the succeeding wave, whose 

 force was thus in a great degree expended before reaching the wall. Thus 

 the greater the original wave, the gn ater was the resisting force of the mass 

 of water, forming as it were a cushion for receiving the succeeding wave ; 

 and though the shingle beach had sometimes been driven in during heavy 

 gales, no injury had ever been done to the masonry of the wall. There 

 might be local or engineering peculiarities in the construction of this pier, 

 which had, 'perhaps, escaped him; and he suggested that it would forma 

 good subject for a communication to the Institution. 



Mr. Walker agreed in the impracticability of laying down abstract rules 

 for the forms of construction of sea defenses, suitable for all situations, 

 when so much depended upon the local position, the force acting upon them, 

 the direction of that force, and the quality and dimensions of the material 

 of which the defenses were constructed. The engineer must, in all cases, 

 after considering the whole of the circumstances, combine his plan in ac- 

 cordance with scientific laws and practical experience, without attempting to 

 fit an empirical formula to all cases, however dissimilar. In many instances, 

 nearly vertical walls cost less than long slopes, and this would be the case 

 when the materi^ds were expensive, from the distance they had to he con- 

 veyed. On the other hand, whenever the materials were close at hand, and 

 EO situated that an inexpensive kind of labour sufficed for placing them, long 

 slopes would be least expensive. Combinations of the two systems had fre- 

 quently been proposed, as in the original design for the Plymouth Break- 

 water, which was, that it should be composed of rough hewn blocks, thrown 

 down upon a base of 70 yards wide, in a depth of 5 fathoms, rising to a 

 width of 10 yards on the top, at 10 feet above the level of low water of 

 spring tides, up to which point the materials were supposed to form a slope 

 of about 3 to 1, and above it a nearly vertical wall of hewn stone was to have 

 been built. The action of the sea upon this work, in carrying a large quan- 

 tity of the stones from the seaward slope entirely over the breakwater, and 

 lodging them on the beach, showed that the inclination should he increased ; 

 accordingly, slopes of 3 to 1 for the land-side, and of 5 to 1 for the sea-side, 

 were adopted, and had been since adhered to in the subsequent works, a 

 long foreshore being at the same time formed. At the western extremity, 

 a buttress of hewn stone at a less inclination than the other parts had been 

 constructed under the directions of Mr. Walker; great pains were taken 

 with the construction, the whole being bounded vertically from the bottom 

 to the top, as well as horizontally, by dovetailing the stones and crossing the 

 joints in both directions, in order to render it nearly a monolylbic mass. 

 The result of this was, that it had perfectly resisted all the action of the 

 sea for the last six or seven years, when considerable injury had been re- 

 ceived by the other ports. At Dover, the part of the works now executing 

 for the commencement of the Harbour of Refuge, was a wall with an inclina- 

 tion of only i horizontal to 1 vertical, in order to enable vessels to load 

 and unload alongside it, and the main body of the work would be only at a 

 small slope. At the Channel Islands, where fine materials were clo.se at 

 hand, but labour was expensive, a long slope was intended to be adopted up 



to the level of low water, and then a nearly vertical wall. At Harwich, all 

 the defenses were laid at a long slope, having respect to the cost of materials 

 and labour. Great discrepancy of opinion existed as to the rising of seas 

 ai^ainst nearly vertical walls. From lengthened observation, Mr. Walker was 

 induced to believe that in very deep water, where the direction of the wall 

 coincided with that of the prevailing wind, the waves would not rise high 

 upon it ; but when the face was ai a right angle to the sea, it would strike 

 heavily and rise high. This subject had been recently treated very ably by 

 Sir Howard Douglas,' and bis arguments in favour of long slopes were based 

 upon sound scientific reasoning, and practical examples, which eiititlcd tliem 

 to much respect. Mr. Walker must repeat, that in practice, engineers must 

 not expect to apply successfully any general rules in all cases ; but must act 

 from the dictates of their own reason, aud the experience of former works 

 under similar circumstanoes. 



7 See ' Journal,' IS.)7, Vol. X., p. 21.'), 2-Jl, 281. 



COALS FOR THE STEAM NAVY. 



Second Report on the Cauls Suited to the Steam A^avy. By Sir 

 Henry De La Beche, C.B., F.Il.S., and Dr. Lyon Playfaie, 

 F.R.S.^ 



The manner of conducting tlie experiments is so fully described 

 in the last Report, that it would be unnecessary again to notice it 

 in detail. It may, however, be desirable to remark, that the in- 

 quiry has been conducted to the best of our abilit)', with the view 

 to its practical utility. 



The main points to which attention has been directed are — 

 1. The evaporati\e value of the fuel: 2. Its mechanical structure: 

 3. The bulk or space which it occupies in stowage: and 4. The 

 chemical identiiieation of the coals operated upon. With regard 

 to tlie experimental determination of the evaporative value of the 

 coals, the same processes have been followed as described in our 

 first Report. Every attention has been been paid to the peculiar 

 characters of each fuel as exhibited during its burning. 



It is well known that particular coals require special modifica- 

 tions of the grate, and even of the boiler, to obtain tlieir maximum 

 result. To acquire this knowledge, it would have been necessary 

 to try every different kind under such varying conditions; and it 

 would have been useless, unless a series of experiments had been 

 made, to ascertain the special circumstances most favourable to 

 the coal under examination. The expenditure of money and time 

 which such a course would have involved, rendered its realization 

 quite impracticable. It was, however, possible so to regulate the 

 draughts of air as to produce those most favourable to tlie pecu- 

 liar cliaracters of each coal. 



To obtain these conditions, each coal was subjected to experi- 

 ment for three successive days, the draught being rtiiferently ar- 

 ranged for each day. Tliis course was also pursued in the experi- 

 ments for the first Report. It would have been eas}', and it might 

 have given the experiments a fictitious appearance of additionHl 

 value, to have performed all the work of the three days under the 

 same conditions, as the results would have been accordant. But 

 such agreements, while they confirmed the accuracy of the experi- 

 ments, would have been of no practical value, since they would 

 not Iiave furnished the data necessary to determine the evaporative 

 powers of the coals under varying circumstances of altered 

 draught. The experiments havej therefore, been tried with dif- 

 ferent draughts, either in the proportions of 4:5:8, or wlien cir- 

 cumstances rendered it advisable of 1:2:4. By experiments with 

 the varying draughts, it became easy to ascertain when the gases 

 escaping from the coals were most economically consumed. The 

 mean of the three days' trial gives, however, more correctly, tlie 

 average evaporative value in steam-vessels, where the exact 

 draught depends, to a certain extent, on circumstances over which 

 the engineer has little immediate control. 



The coals most liable to be influenced by the different adjust- 

 ments for the admission of air, are those wliich, from their 

 bituminous characters, are most apt to generate a large quantity 

 of gaseous products on the first application of heat, sudi as the 

 coals from the Nortliumberland, Durham, and Lancashire coal- 

 fields: and it has therefore been found, tliat the experiments made 

 with them, under dift'erent areas for the admission of air, vary 

 much more considerably than with the less bituminous coals of the 

 South Wales coal-field. It has even been found necessary in the 

 highly gas-giving coals, such as the Cannel coal of Wigan, to 

 allow air to enter behind the fire-bridge, so as to complete the 

 combustion of the escaping gases. 



Experiments were made at the suggestion of the late First Lord 



* An abstract of llie first Report was given in tile C,E, Hi A. Jjiirnai, la-14. Vol. XI., 

 p. 273. 



