Rq)ofl of ~he Ommissioners ,qppointed to Inquire into the .3Tplication of Iron to Railway Structures.*From the infonm ~ion supplied to us, it appears that the proportions and tbrms at present employed for iron structures, have been generally derived from numerous and careful experiments, made by subjecting bars 0fwroug!~t or east iron, of different forms, to the action of weights, and thence determining by theory and calculation such principles and rules as would en, able these results to be extended and applied to such larger structures aild loads as are required in practice. But the experimentsLwere made by dead pressure, and only apply therefore to the action of weights at rest. On the contrary, from the nature of the railway system, the structures employed therein are necessarily exposed to concussions, vibrations, torsions, and momentaff pressures of enormous magnitude, produced by the rapid and repeated passage of heavy trains.These disturbing causes, in smaller degree, have always occurred in structures connected with mill-work or other mechanism. But the effects upon their stability have not been found greater than could be met t)y increasing the dimensions of the parts without especially inquiring into the exact principles upon which such increase should be made. Thus~ we are infbr,ned that the dimensions of cast iron girders, intended for sustaining stationary loads, such as water-tanks and floors, are usuallyso propor-tioJ~ed that their breaking-weight shall be three times as great as the load they are expected to carry, or in some cases four or five times as great. llut when the girders are intended for railway bridges, and therefore sub-" From the London Civil Engineer an(i Architect'
Xo reliable data exists, at the present time, to show the exact effect of speed upon the coefficient of friction between shoes and wheels of other materials than those described in these experiments ; such information, however, as can be secured, indicates that, while the values of the constants a and b, in the above formula, may vary for brake shoes and wheels of other materials, the general effect of speed upon the coefficient of friction is the same ; that is, the friction is greatest at very low speeds, and decreases, by the same general law, as the speed increases. The results shown in Table X, on page 172 of the third paper, uniformly indicate that, at any constant speed, the friction also diminishes, according to some law, as the time of rubbing of the brake shoe upon the wheel is extended. The extent of the experiments in this direction is somewhat too limited to determine, as fully as is to be desired, the effect of the time of continued rubbing upon the coefficient of friction. Yet it is apparent that, however long the brake shoe continues to rub upon the wheel, the friction can never become reduced to zero, and the general relation between the coefficient of friction and the time of continued rubbing must therefore be expressed by an equation similar to that for the coefficient of friction as effected by speed.
Xo reliable data exists, at the present time, to show the exact effect of speed upon the coefficient of friction between shoes and wheels of other materials than those described in these experiments ; such information, however, as can be secured, indicates that, while the values of the constants a and b, in the above formula, may vary for brake shoes and wheels of other materials, the general effect of speed upon the coefficient of friction is the same ; that is, the friction is greatest at very low speeds, and decreases, by the same general law, as the speed increases. The results shown in Table X, on page 172 of the third paper, uniformly indicate that, at any constant speed, the friction also diminishes, according to some law, as the time of rubbing of the brake shoe upon the wheel is extended. The extent of the experiments in this direction is somewhat too limited to determine, as fully as is to be desired, the effect of the time of continued rubbing upon the coefficient of friction. Yet it is apparent that, however long the brake shoe continues to rub upon the wheel, the friction can never become reduced to zero, and the general relation between the coefficient of friction and the time of continued rubbing must therefore be expressed by an equation similar to that for the coefficient of friction as effected by speed.
THE Sanitary Institute has made it one of its duties to provide an address to the working-classes of the town in which it holds its Annual Congress. And it has been allotted to me, as Chairman of the Council of the Sanitary Institute, to address you on this occasion. If it were necessary to assmne a title for my address I would select the motto of a kindred society, viz., the National Health Society, which is, &dquo; Prevention is better than Cure.&dquo; For we sanitarians hold that the health of a nation depends very much upon the will of the nation. More than one-half the diseases from which we suffer, and more than one-half the deaths, arise from causes which we sanitarians say are within ougrown control. The present is an occasion of more than usual importance, for not only does the nea.r approach to our shores of a dire epidemic, the cholera, compel us to direct our attention to the progress of sanitation in this country, but Parliament and the public have at last awakened to the fact that a large portion of the working classes of this country have been, and still are, permitted to live in wretched unhealthy dwellings, and an Act of Parliament has been passed for amending the law relating to the housing of the working classes. ' These two subjects are closely related to each other. There are many people who assert that we have made so much progress since the last visitation of cholera to this country that we may now hope almost entirely to escape from its ravages. I earnestly wish I could believe that it might be so; but when I
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