1842.J 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



229 



EXPLAKATION OF TaBLE. 



No. I . The girders were laid together in pairs, with a block of iron between at 

 each end, and squeezed together, and the diminution of the distance between 

 the two girders was divided as the deflection of eacli. Before the pressure 

 was applied, parallel chalk lines were struck at a small distance apart, to 

 ascertain the position of the neutral axis, which was found to be nearly in 

 the centre of tlie depth. The bearing was 9 in. from each end, and the 

 pressure applied in the middle : the girders were kept from goiug back to 

 their natural position by a strong loop of wrought iron embracing them both. 

 The girders were elliptical on the upper edge or back, and horizontal on the 

 lower edge ; they were also strengthened on the upper edge, and had a broad 

 flanch at bottom, and sometimes a flanch at both top and bottom. The 

 whole of the girders, except No. 14 in the first table, were used at the 

 Oxford and Cambridge Club. No. 14 was also used in the construction of 

 the City of London School, Cheapside. After the above experiments, the 

 architect in his next work, the Judge's Chambers, abandoned the fillet at top, 

 and diminished the thickness ; as for example, a girder of the same length 

 of bearing as No. 1 in the first table had a uniform thickness of I J- in., 

 depth in centre 15 in., at end 10 in., breadth of bottom flanch 4 in. : the 

 girders at the last-named work were not proved. 



No.3. Mr. Wood calls the three divisions of the section " top, rib, and keel," 

 the rib being the portion between the top and keel, for which two last terms 

 I have substituted the words fillet and flanch, and for the whole three terms 

 I have the extreme depth. No. 6 is the only rail that was parallel, which 

 weighed 43 lb. per yard, and No. 4, which weighed only 32 lb. per yard, was 

 elliptic or fish bellied : it retained its elasticity as long as No. C, with an 

 equal weight. 



Mr. Wood gives one table of experiments of east iron rails, the average 

 weighing 55 lb., 3 ft. 9 in. between supports, being straight on the upper 

 edge, and parabolic on the under edge ; extreme depth in centre C in., at end 

 4 in.; breadth at top 2:^ in., tapering away to 1=^- in the middle, and swelling out 

 at bottom into a square, each side being | of an inch, and the diagonal being 

 vertical, broke with 5| toi»s ; and he observes that cast iron is very rigid, 

 and deflection trifling before fracture, and that by mixture of metal, so as to 

 increase its specific gravity, the same rails took Ijtons more weight to 

 break them. 



The following are from experiments which have not bteu published. A 

 rail of cast iron, straight on top, elliptic on bottom, edge 7 in. deep in 

 centre, 3^ in. at each end ; flanch at top 2^ in. x IJ in., at bottom li in. 

 X li in. and ^in. thick in the middle ; with 5 tons, in the middle deflection 

 was apparent ; distance between supports 3 ft. 8 in. 



At 7 tons, the deflection was yub of ""i inch- 



9 

 10 

 II 

 12 



m 



■Si 



I) ^ „ Broke instantly through its 



centre. 

 Another cast iron rail, 2 ft. 8 in. between supports ; 5 in. in middle, SJ in. 

 at each end, and ^ thick ; flanch at top 1 J in. < 1 in., at bottom 1 J in. x | in. ; 

 broke with 8^ tons ; fracture in the middle, and nearly perpendicular. 



St- Ann's, Newcastle-npon-Tijne. 0. T. 



LIGHTNING CONDUCTORS. 



A paper on lighlning conductors, in connexion w itli the accident at Rrix- 

 ton Church, was lately read at a meeting of llio London Kleclrical Society. 

 Its aullior, Mr. M'alker, the secretary of the society, bad made a survey of 

 the damage done to the tower of Brixton Church, and found in it so practical 

 an illustration of Dr. Farailay's opinion on the "lateral discharge," as to 

 induce him to investigate the subject more closely. It seems that no ar- 

 rangement of metals could have been better adapted than that met with in 

 this steeple to invite a flash of lightning to do mischief. There was a regular 

 series of stepping-stones, as it were — first, an insulated metallic cross, then 

 twenty feet of stone work ; in passing this interval the roof of the lantern 

 was shattered. Then come twenty or thirty feet of conductor, in the form 

 of the clock wire, and a water pipe ; and then a break of twelve leet. Here, 

 again, was an explosion, and an immense mass of masonry was shattered 



away from the base of a column intervening' between the termination of the 

 water-pipe and the commencement of the next series of conductors. Within 

 the belfry a " lateral discharge " took place ; the fluid passes from one con- 

 ductor to a vicinal one for no other reason than to obtain a wider path. The 

 author showed that electricity not only chooses a short but also a wider 

 path ; and that the "lateral spark" arises from the latter property. He then 

 explained that it is not enough to have a continuous or an insulated lightning 

 rod ; but it is most important to have it far away from other metallic bodies; 

 for however capacious the rod may be, and however adapted to convey, not 

 only what passed down it. but ten thousand times more, yet, if another con- 

 ductor is near, a ilash will pass between the two, and ignition of neighljouring 

 combustibles will be the result. Fortunately, in the case in question, only a 

 small part of the whole fluid passed « itliin the tower, consequently the lateral 

 explosion'w as not severe. As it is not always possible to place lightning rods 

 entirely out of the neighbourhood of other conductors, Mr. Walker showed 

 that the possibility of the fluid's passing between them should then be con- 

 verted into a certainty by making metallic coiumunication between them, and 

 thus tracing out a path along which the fluid might pass without the de- 

 velopment of light and heat. He spoke of the peculiar property of the points 

 of leaves, twigs. Sec, in drawing oft" quietly charges ni electricity, and stated 

 his conviction that tall trees would always be found valuable, if not in en- 

 tirely averting, at least in greatly mitigating the force of a lightning shock. 

 The theoretical opinions given in this communication were based upon the 

 experiments of the Royal Institution, the object of the author being to show 

 how closely they were illustrated on the grand scale of nature, and to direct 

 the attention of the public generally to a closer study of the properties of 

 lightning-rods, a subject on which, perhaps, more than on any other prac- 

 tical point, more ignorance prevails than can be well conceived. 



EXPERIMENTS AT WOOLWICH ON COAL- BOXES OF STEAM 

 VESSELS. 



On 11th May a large detachment of the Royal Artillery attended in the 

 Marshes, to make experiments with powerful gunsag.ainst the erection repre- 

 senting the side of a steam vessel, and the coal box. The experiiueuts 

 commenced at a range of 1250 yards, with 68-pounder and 56-pounder gunsj 

 Colonel Dundas' 110 cwt. gun requiring 181b. of powder to each charge, 

 and Mr. Monks' 97 cwt. gun requiring IG lb. of powder each charge, made 

 excellent shots, but failed in passing through the coal-hox, although the iron 

 composing the interior portion of the case was rent for several inches where 

 the balls had struck, and where they were retained, having evidently ex- 

 pended the greater portion of their force in passing through the coals. This 

 result was rendered certain by the effect of one of the balls, which had 

 passed through the portion of the erection extendmg beyond the coal-box, 

 driving before it a solid piece of the wood, 12 in. square, and about G or 7 ft. 

 in length, and ultimately passing through a similar thickness of wood in the 

 rear, sinking deep into the earth composing the butt. There were three other 

 guns, 5G-pounders, respectively of 85 cwt., 81 cwt., and 67 cwt., in weight 

 each, fired during the first six rounds, but they were then discontinued, and 

 the practice carried on with Colonel Dundas' and Mr. Monks' guns, but they 

 failed in destroying the coal-box to any greater extent than has been stated. 



The experiments were resumed on the following day with Mr. Monks' 

 56-pouuder gun, weighing 97 cwt. The officers in command were so satisfied 

 with its practice, that it was ordered to discontinue firing after the 21th 

 round. Several of the shot entered the coal-box, and caused great destruc- 

 tion ; and although they did not pass through, they tore the joinings from 

 the bottom to within about two feet of the top. T\\ o more rounds were fired 

 from the 68-pounder, one of which rent tlie joinings at the east end of the 

 coal-box from the bottom to within about three inches of the top, and a great 

 quantity of the coals fell out. The experiments with these guns, which were 

 made at the long range of 1250 yards, having been concluded, General 

 Millar's 10-inch gun commenced practice, having been previously pl.'.ced at a 

 range of 9(.0 yards. The firing from this gun with shells was the best that 

 could have been witnessed. The first shell entered the centre of the bull's 

 eye, but did not explode, probably from the action of the loose coals through 

 which it passed extinguishing the igniting composition before it could com- 

 municate with the contents of the shell. The secor,d shell entered within 

 about two feet of the bull's eye, and did not explode, prob;ibIy from the same 

 cause as in the former case. The th-rd shell entered about nearly the same 

 distance from the bull's eye as the second, only nearer the ground, and in six 

 seconds exploded, throwing up into the air a flame of ignited small coils to a 

 height of upwards of 30 It., forming a grand and imposing spectacle, and 

 scattering fragments of the shell, wood, and coals, to a distance of 200 yards 

 in all directions. A fourth shell was fired, but it entered and exploded in the 

 butt. 



The experiments were again resumed on the following Friday, w hen it was 



2 K 



