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SUPPLEMENT TO PRACTICAL GLEANINGS,
FROM THE TRANSACTIONS OF THE MANCHESTER MEETING OF THE BRITISH ASSOCIATION
ON THE ACTION OF LIGHTNING CON
DUCTORS. BY CHAS. WALKER, ESQ. [Abstract of a paper read before the London Elec
trical Society, July 19th, 1842.] The object of an extensive series of experiments related in this communication is to illustrate the following opinions :
I st. --- That the discharge of a Leyden jar does not resemble a flash of lightning ; and, therefore, that Leyden jars should not be employed in investigating the action of lightning rods.
2nd.—That the discharge from a prime conductor does, in all essential points, resemble a flash of lightning ; and is therefore admissible in such experiments,
3rd.—That a wire, on which sparks are thrown from a prime conductor, represents a lightning-rod.
4th.—That sparks will pass off from such a wire, and, therefore, from a lightning-rod, to vicinal conducting bodies ; and,
5th.—That these sparks may be prevented by connecting the vicinal bodies with the rod itself.
The experiments were made by aid of the magnificent machine of the Polytechnic Institution, and are supported by a course of reasoning based upon the dissimilarity between the Leyden light and a lightning flash, and the resemblance between the latter and that from the prime conductor. It was shown that the length of the spark from the conductor is due to the action of one force in one direction ; and that the shortness of the Leyden discharges is due to two forces, acting in opposite directions. The importance of excluding the Leyden experiments from the field of inquiry is very evident from the fact that on them hinges a large portion of the conflict of opinions. Using the new prime conductor and throwing sparks from it upon wires subjected to every variety of arrangement “lateral sparks” were always obtained, unless vicinal bodies were in close metallic connexion with the wire conveying the charge. This fact was illustrated by a most important modification of the wellknown experiment with the metallic discs ; and if this modification, which consis'ed in erecting an elevator rod beneath the great globe, forming the prime conductor, be legitimate, the danger of lateral flashes is evident.
Mr. Nasmyth brought forward (27th June) several specimens to illustrate some remarks which he intended for further illustration of his previous observations on this subject. (See Mech. Mag. No. 987, p. 34.) From late accidents, arising from breaking axles, the public were alive to the subject, and it was desirable that the question should be examined. In locomotive engines the axle was the chief point of danger; and it was therefore important, both as a scientific and practical question, to determine the nature and habitude of iron when placed under the circumstances of a locomotive axle. Experiment was the only way to discover this, and he would have wished to place iron under exactly similar circumstances; but the short time intervening since the previous meeting, had rendered it impossible to do so. One opinion then was that the alternate strains in opposite directions, which the axles were exposed to, rendered the iron brittle, from the sliding of the particles over each other. To illustrate this, Mr. Nasmyth took a piece of iron wire and bent it back and forward, it broke in six bends. He had suggested annealing as a remedy for this defect : in proof whereof, he took a piece of annealed wire, which bore eighteen bends, showing an improvement of three to one in favour of annealing. He should therefore advise railway companies to include in their specification, that axles should be annealed; he did not like the custom of oppressing engineers with useless minutiæ in specifications, but this was so useful and so cheap, that he consi. dered it ought to be insisted on. To exhibit on a larger scale the effect produced on iron in our workshops, he showed a specimen of iron as it came from the merchant: being nicked with a chisel, it broke in four blows with a sledge, at the temperature of 60°, with a crystalline fracture ; by raising the temperature 40° higher, it bore twenty blows, and broke with the tibrous or ligneous fracture; so that the quality of iron was not the only circumstance to be considered as influencing the fracture. I noticed also, said Mr. Nasmyth, at the last meeting, the injurious effect of cold swaging, as causing a change in the nature and fracture of the iron; and here let us take the practical workshop view of the case, and not run after the ignis fatuus of electricity or galvanism, but consider the practical effects. Swaging was necessary in many cases ; for instance, when an axle had collars welded on, these could not be finished
with the hammer, and certain tools called fibres were cut, which supported more of the swages were used, from the action of which weight than the compressed.—Mr.Worthinggreat condensation of the iron took place, ton thought the additional friction in steps, and a beautiful polish was given to the sur given by annealing, would counterbalance face, with what injurious effect he would the advantage gained in strength, as caseshow by the next specimen, which had been hardening (the very opposite operation) was heated red hot, and then swaged till cold; it used to diminish friction, by giving a glassy broke at one blow without nicking, and the hardness to the surface, the annealed axles fracture was very close and beautiful, like would be laid aside after a few trips, from steel. This showed the fallacy of consider the friction : he would wish, as a security ing close fine grain a good test of excellence for life, that the springs should be made as in wrought iron; but moderate swaging was long as possible, to diminish the effect of often necessary, and not injurious, unless concussion.—A Member showed specimens where an over regard to finish carried it to of pins which had broken in machinery. excess. To prove that annealing restored They appeared very crystalline in fracture ; the toughness and fibrous texture, a portion the bar from which they had been made was of the last bar was heated, and cold-swaged fibrous and tough: showed also specimens till cold as before, then heated dull red, and of tender axles broken on the Sheffield and left to cool gradually ; it bore 105 blows Rotherham railway. Tender axles most frewithout breaking, and at last was rather torn quently broke from the action of the brakes asunder than broken, as was shown by the on the wheels ; crystals larger in the centre specimen ; this proved that the fibrous struc of the axles than at the ends.—Mr. Mallet ture was restored by annealing, and he there was quite at issue with the French committee fore thought it should be insisted on in on the very uncomfortable Report which specifications. The effect of heating to weld they had made so authoritatively; he being-heat was very injurious, unless the iron lieved that the alternate strains, as long as was subsequently hammered to close the tex they were within the limit of elasticity, did ture ; a piece of the same iron heated to not injure the texture of the iron. Wire welding, and left to cool, broke without might be bent backward and forward to ipfinicking, in one blow, showing very large nity, if we kept within this limit. The effect crystals, especially in the centre. The effect of nicking depended on a change of crystalof nicking was also very singular. The line structure; that the effect of the nick strength of iron was generally stated to be in determining fracture, was according to the equal to its sectional area ; but a nick not sharpness of the chisel, and the direction; a removing ito of the area took away it of the nick sloping, according to the natural direcstrength. Mr. Nasmyth broke a piece of tion of the fibre, was not so efficacious ; a nicked, or rather scratched wire, to illustrate molecular change was effected by this cutting this point. These, and similar things, did across the fibres : we, in fact, established a not prove that science and practice were at plane of cleavage in the iron; this took place issue; but, as Halley reached the great accu in glass, when scratched with a diamond, racy of his prediction of the return of his although glass, from passing through the incomet by taking into account the disturbing termediate viscous state, did not crystallize forces of Jupiter and Saturn, and the other so definitely as iron, which crystallizes per planets amongst which the body had to pass, saltum. Iron, polished and placed in such a so scientific men should seek in the work. situation as just not to corrode, if scratched, shops correctional formulæ, by learning there immediately began to corrode ; and iodide the practical occurrences which would eluci,
of mercury presented a curious example of date their theories, and he hoped that these entire disintegration from a slight scratch, specimens might be of some use.
Crystallization takes place in the direction Prof. Willis was aware that many subjects of motion; in rolled iron the motion was in of a purely physical nature could only be the direction of the length of the bar or plate, explained by practical research ; and one and percussion, in a direction perpendicular great advantage of the British Association to that, had the effect of breaking up these was, that it brought scientific and practical laminæ or fibres of crystals, into their origimen together for this purpose.-Mr. Fair. nal molecular arrangement; and this effect bairn was of opinion, that the two chief was proportionate to the temperature caused, causes of breaking axles seemed to be bend. and extent of motion imparted. But he being and percussion, changing the fibrous into lieved, that to effect this molecular alteration the crystalline structure; this last was the required more violence than was to be exetiect of cold swaging, and he hoped that his pected in any ordinary railway travelling, or, friend Mr. Hodgkinson would undertake a indeed, any circumstance of machinery in series of experiments on this very interesting perpetual work. The chicf danger was to subject. By nicking & bar the extended be feared where any cutting perpendicular to
the direction of the fibre took place, as, for instance, shafts, with square collars, would break at these collars, while a little rounding out preserved them. That rotation of iron induced magnetism, he was aware, but he did not believe that either rotation or vibration would affect iron which was sound when first applied. If this theory were correct, the engineer should discard wrought iron entirely; no engine was safe, no suspension bridge should be trusted.-Sir J. Robison considered that injuries did arise from vibra. tion and alternate bending; he instanced tongues of musical instruments, and the effects of bending pure tin, which crackled and broke when very slightly bent in opposite directions. Mr. Mallet believed those tongues to be alloyed, and he found that alloys altered their crystalline nature from mere lying by, as tough brass became brittle, &c., which did not happen in simple metals.—Mr. Nasmyth showed that the effect of hammering bars was actually to make them hollow ; every stroke had a tendency to make the bar an ellipse, and the intersection of all their axes was apt to be a hole, from the sliding of the laminæ over each other.
broke with 6 blows, ditto Scrap, 3 blows, ditto hot blast, 1 blow; again, Low Moor cold blast 18 blows, Bierly, ditto, 18, hot blast of as good materials, 3 blows; again, Elsicar cold blast 21 blows, Milton hot blast lblow; therefore, in iron for axles this difference of at least ath of the strength was very important. As to scrap iron it bore too high a character. Scrap, made on the old plan, was all charcoal iron, but the mo. dern scrap iron was very inferior, being 328. 6d. per ton cheaper, so that ironmasters put off as much of this cheap material as possible. Hot blast iron was rejected now for water pipes, &c. and even for cannon balls; and, in fine, he had been told by very eminent marine engine makers, that where any percussion took place, hot blast cast iron was only half the strength, and wrought iron only 4th the strength of cold blast.—Mr. Fairbairn explained, that he had found great difficulty in obtaining specimens from the different iron-masters, who would of course send, when possible, the best specimens, but every care had been taken to insure accuracy in the experiments.-Mr. Hodgkinson said, that the average strength of hot blast had been 1 do weaker than the cold, but the inferiority was chiefly in the softer irons; as the hardness increased the two kinds approached to equality, and in the hardest irons the hot blast was the best. He thought his experiments, made without any interest on either side, and with the greatest care, were more to be depended on than experiments made by those who had an interest in the result.Prof. Vignoles explained, that the question of hot and cold blast had nothing to say to the late contract for cannon balls.
THE HOT AND COLD BLASTS. Mr. Fairbairn read his Report On Experiments on the Transverse Strength of hot and cold blast Iron.'— The bars, as described in the former Reports, were supported by standards, 4 feet 6 inches apart, and were loaded with different weights; they were occasionally carefully examined, and showed a very slight progressive deflection. He had no doubt that they would ultimately break, but the progress was very slow. He read a table showing the weights laid on, and the deflections of each bar.
Mr. Hartopp said, that Mr. Fairbairn's former experiments on hot and cold blast iron, had created a false impression with regard to the strength of hot blast iron. Mr. Fairbairn had found very little difference between the hot and cold blast ; but his experiments, made with great accuracy, and in which the weights were laid on with great care, were of little practical advantage, as these were not the circumstances under which iron was tested in practice : there percussion, violent and sudden impact, should be expected, and here lay the great deficiency of hot blast iron. Even in Mr. Fairbairn's experiments, Oldberry, No. 2, cold blast, bore twice the percussion of Oldberry hot blast ; and Milton hot blast was only half the strength of Elsicar cold blast, made of the same ore and smelted with the same coal. Experiments had been made in Yorkshire with great care ; the results being, Low Moor cold blast bar iron, 3 inches diameter,
STRENGTH OF MATERIALS. Mr. Hodgkinson explained his apparatus for trying the strength of materials. He brought his apparatus forward, as he had made many experiments; and he was desirous to render them as trustworthy as possible, by convincing the members that every care had been taken to insure accuracy. Other experiments had been rendered unworthy of reliance, from injudicious methods of affixing the testing apparatus-as those of Rennie and Capt. Brown on iron ; Girard's experiments, &c. In crushing specimens, it was necessary that both ends should be well bedded, and the pressure transmitted through the axis. To this, other experimenters had not always attended, and by using the pres. sure of bores directly on the substance to be crushed, they introduced the different errors arising from the pressure being oblique, transmitted through the side, or being exerted on mere points, instead of equably exerting its force over the entire top surface :
to obviate these objections, he had devised
RIVAL RAILWAY SYSTEMS - RAILS apparatus by which all these errors were
WITH CHAIRS AND avoided. Mr. Hodgkinson explained the Professor Vignoles read a paper “ On the crashing apparatus by drawings, &c. In best Form of Rails, and the Upper Works esperiments on tearing asunder, he had also of Railways generally."--He wished to com. taken great care, by means of apparatus, pare the two chief systems of laying down which he exhibited and explained, that the rails, with chairs and without, and to do so strain should be through the axis, and other he referred to two diagrams :-No. 1, exvise free from causes of error. Mr. Hodg. hibiting the heavy rail and heavy chair used kinson explained his experiments on torsion, on the South-Eastern Railway, the weight of and illustrated his observations throughout rail being 80 lb. per yard, and the chair 20 lb. : by many models and specimens of the sub the rail was fastened in the chair, not with stances on which the experiments had been iron, but with a longitudinal plug or key of made.
wood; this mode of laying rails was found Professor Moseley asked whether, in the to answer very well.-No. 2 was invented experiments on beams, care had been taken by Mr. Evans; it was rolled with a slot or to obviate the effects of the friction of the groove running along its under side ; this beams on the supports, as this would affect slot, after coming from the first rollers, was the direction of pressure, altering it from rendered dovetailed by compressing the bot. vertical to inclined, and the neutral line only tom edges of the rail towards each other, passed through the centre of gravity of the thereby narrowing the slot at the bottom. beam when the pressure was vertical : also These rails required no chairs, having a conif care had been taken in laying on the tinuous bearing on longitudinal wooden weights, as a weight suddenly laid on pro sleepers, being fastened down by bolts, with duced mathematically twice the effect in de dovetailed heads slid into the groove, and flection. Theoretically, the weight should which, passing through holes in the timbers, be increased by small additions, even as were secured with a nut and washer at the grains of sand.—Mr. Hodgkinson said he under side. He had suggested this improvehad taken all precautions with regard to the ment, as they had been previously fastened weights ; they were added by small portions, with a cotter. By this method, all the dif. and with great care; the beams rested on ficulties attendant on fastening down the tolerably smooth cast-iron, on which he be chairs were removed. The chairs had been liered the friction would be of little im. fastened with bolts and screws, but he had portance.
found that on the slightest loosening the
bolt.heads flew off, from the continual perBROCKEDON'S CAOUTCHOUC STOPPERS FOR cussions, and the screws very soon allowed
vertical play, from the yielding of the fibre Mr. Brockedon exhibited specimens of his of the wood. By Evans's rail, we secured patent India-rubber stoppers for bottles, ex the rail without the intervention of the fibre plaining the late improvements in the con of the wood. One inconvenience attending struction of the cores on which the India. it was, the trouble of scraping away the rabber is spread. The present cores, he earth to tighten the nuts when necessary; said, were made of cotton twisted into but this might be partially remedied by strands, &c., by means of a machine which placing the bolts as often as possible in the he explained by a diagram. The cylindrical transverse gutters for draining the road, by rope now consisted of several strands of which at least one-half the bolts might be tightly twisted cotton, lapped with flax easily got at; and the difficulty of tightenthread, and laid together longitudinally, ing the remaining bolts would be lessened, loose fine cotton rovings being placed be it, as he recommended, the timbers were tween them ; the entire was then lapped in left uncovered. He preferred thus giving a a cylindrical form with flax thread, attaining free circulation of air, and disliked burying by this method the advantages of perfect the sleepers in ballast. The weight of Evans's roandness and firmness ; they also gave suf rail was only 45lb. per yard, although quite ficient bold to the corkscrew, and bore the strong enough, while the other was 100lb. beating process well. These stoppers would The bevel in No. 2 rail might be given in slide on glass when wet, but not when dry, the wood-bearing; in No. 1 it was caused (although there was no cohesion in this latter by the casting of the chair ; this latter rail, state,) so that the bottler, by slightly wetting from having its top and bottom sides alike, these stoppers with the liquor which he was had this advantage, that when it began to bottling, could easily insert them; and when wear it might be turned round, or even turned this slight film of moisture was dried up, the upside down, which was a very great advanstopper required considerable force to with tage. He had for many years advocated draw it.
wooden sleepers versus stone, from his ex. VOL, XXXVII.
perience on the Dublin and Kingstown Railway, where he found that the granite sleepers, the more massive they were the more injurious to the rails and carriages. These had all been taken up, and wooden sleepers laid down, and the saving in expense of repairs would in a few years reimburse the outlay. The railway costs now only 501. per mile per annum for repairs, notwithstanding the great traffic over it. The rails were the old 421b. rails, and, nevertheless, were still used, in consequence of the advantage gained by the wooden sleepers. He recommended keeping Evans's rail to the gauge by light iron rods passed through holes in the rails, and secured by nuts : he thought these transverse ties should never be used as supports.
Mr. Bucke remarked, that the rails on the North Union had already been so worn as to require turning. The section of Evans's rails was bad, as, from the squareness of the top, the wheel would not bear on the centre of the rail. He had used these rails a little himself, and had no objection to them for light work. He had remedied the form of rail on the Manchester and Birmingham Rail. way, so as to give the wheels a bearing on the centre of the rail. He conceived a great disadvantage in the longitudinal continuous bearing was, that the foundation was so near the surface; the stability of the foundation was as the square of the depth, and therefore the necessarily narrow foundation of the continuous bearing was rendered still weaker by its proximity to the surface, and the plan of laying down a railway “ like a ladder on the ground," had failed where it had been tried. -Prof. Vignoles considered that the failure to which Mr. Bucke alluded, was from making the transverse ties too strong.-From the Athenæum.
and P 35424.949 + 4910 = 7.21486. Hence, P = 7 21486 + 1 8.21486 is the present value of an annuity of £1 for 10 years for an age of 23, the first premium being paid in advance.
[We have made another computation from a formula given in a former Number of the Magazine, and it is exactly the same as the above.]
Let x = required annual premium, , 821486=P. Then 100 x P x R19 x x x will be the probable amount of all the premiums when insured at compound interest for 10 years, and if this sum be improved for 10 years more, it will be 100 x P x R20 x x x, and on the supposition of an equality of probabilities, ihe said sum should be £6933. Hence, P
110 x P x R20 6933
£4,673 821:486 x 1.806111 £4 13s. 5 d., the required annual premium.
By a like process of calculation, the annual premium, when the value of interest is 4 per cent., will be £4 Os. lld.
THE CASE IN LIFE ASSURANCE -(P. 95).
Solution. Sir,-I send you a solution of Iver M'Iver's question on Life Annuities.
First let us suppose the rate of interest to be 3 per cent.
The number living at the age of 23 by the Northampton Tables is 4910, and at 43, 3404 :: 4910 : 3404 : : 100 : 69:33; that is, 69:33 will be the probable number alive at the end of 20 years, and 69.33 x 100 = £6933 will be the probable sum to be divided among the survivors at the end of 20 years.
The next thing to be done is to compute the value of an annuity of £l on the life of a person aged 23 for 10 years.