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me in the wish to raise the working men of this kingdom to a higher state of intellectual culture than they have heretofore attained in their relations to society and the domestic circles by which they are surrounded.

Leaving, however, the question of popular education to abler hands, I would now direct attention to the papers on the Collapse of Tubes, in which will be found not only the first investigation of the conditions of rupture in vessels exposed to uniform external pressure, but also an entirely new law of resistance, fully determined by direct experiments. The results recorded in these papers bear directly on the daily practice of the Engineer. The law that the resistance is inversely as the length of the tube exposed to pressure, is both of great importance and wide application ; in a word, it should be kept in view in every construction where tubes exposed to external pressure form the whole or a part of the design.

In the paper on the Resistance of Glass Globes and Cylinders to Collapse from External Pressure, and on the Tensile and Compressive Strength of various kinds of Glass, I have sought to confirm the previous experiments on wrought iron tubes, by experiments on a perfectly homogeneous material. At the same time, as the mechanical properties of glass have been hitherto little known, the paper has been rendered more complete by experiments on the tensile and compressive strength, which I hope may prove valuable to those who are engaged in scientific investigations. We are still very deficient in our knowledge of the laws of contraction in bodies passing from the fluid to the solid state, and the effect of internal strains arising from unequal contraction on the cohesive strength

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of the material. That such strains exist to an injurious extent is often seen in cast iron, and was found to exist to a still greater extent in the experiments on glass. Let us hope that further researches may be made on this point, and greater certainty secured in metallic constructions, under the influence of temperatures producing in succession the fluid, the semi-fluid, and the solid state.

On the influence of temperature on the cohesive strength of wrought iron I made, some time ago, the experiments recorded in the succeeding paper. These extend from below zero to a dull red heat, and will, I trust, be found of value in showing the conditions in which the material can be trusted when exposed to increased or diminished temperatures.

I have reprinted the paper on the Compressive Strength of Brick and Stone for the guidance of the engineer and architect, and they may safely be relied upon in calculating the strength of piers, walls, and other structures where these materials are employed.

The Lecture on the Machinery employed in Agriculture was undertaken at the request of several distinguished agriculturalists, and amongst them the Right Honourable the Speaker of the House of Commons. In this brief treatise I have endeavoured to point out the defects of our present improved and improving system, and to propose remedies for them. I have especially urged upon the farmer the value and necessity of machine culture, in order to increase the productiveness of the soil, and to secure the crops with greater certainty and despatch. I have directed attention to the state of the land, and the improvements required before machine culture can be effi

ciently employed, and I have concluded with the expression of a belief that the English agriculturalist might be very much benefited by availing himself of the appliances which the present advanced state of mechanical science has placed at his disposal.

The Lectures on the Rise and Progress of Civil and Mechanical Engineering were intended for the information and encouragement of the members of several combined institutions at Derby; they are historical and descriptive, and having been personally concerned in the promotion of some of the works described, I am perhaps better able to supply the material and fill up the gap between the present and that period which belongs to the past history of engineering art.

The Lectures on Iron Shipbuilding are on a question of such deep importance that I make no apology for their introduction into this series. When it is known that the most disastrous and fatal consequences have followed from the construction of vessels on erroneous principles, and that thousands of lives are at the mercy of our naval engineers and architects, assuredly it is essential to the interests of humanity that defects and errors of construction should be pointed out and sounder principles applied. If we examine closely into the state of iron shipbuilding, it will be found that numbers of vessels are built and are now afloat which are perfectly unseaworthy, that our knowledge of first principles is far from perfect, and that a remedy should be immediately applied to avert the calamitous and fatal shipwrecks which so frequently fill the columns of the public prints.

Impressed with the conviction that these lamentable

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catastrophes might be in some cases averted, I was induced to venture on the inquiry, and finding that a want of foresight in the builder, or a want of knowledge of the conditions of rupture of iron vessels on the present principle of construction appeared to exist, I lost no time in applying the results of my own experiments on girders to this case, and submitted my conclusions to the shipowners of Liverpool and the members of the Polytechnic Institute of that town. The same paper was subsequently read before the Institute of Naval Architects in London, and forms the fifth lecture of the present volume.

In the sixth lecture I have applied the same principles to vessels of still larger size, where a modified form of construction appeared necessary. I earnestly hope that the views thus recorded may lead to further inquiry, and subsequently to a class of experiments calculated to ensure safety, and that with a more correct and judicious distribution of the material and more exact principles of construction.

It was originally my intention in the publication of this series to have resumed an inquiry into the properties of steam. This experimental investigation has occupied my attention, along with that of my friend and colleague Mr. Thomas Tate, for the last three years, and although we have arrived at important results in regard to density and expansion, up to 60 lbs. pressure per square inch, we are short of data for extending them to higher pressures and a greater degree of superheating, and the experiments, although in progress, are not yet in a condition suitable for publication. A résumé of the results already obtained will, however, be found embodied in Lecture VIII., e

tracted from our joint paper in course of publication by the Royal Society.

Amongst other constructions of a useful and practical character, I have introduced a description of the tubular cranes, so admirably adapted for lifting heavy goods, and swinging them round over a circle of large radius.

In this statement it now only remains for me to express my acknowledgments to the Councils of the Royal Society and the British Association for the Advancement of Science, for the readiness with which they granted permission to republish some of my papers in the present volume. Also to my friend Mr. T. Tate, who is ever willing to assist me with his superior mathematical attainments. I am indebted to my assistant and secretary, Mr. · W. C. Unwin, for the care he has bestowed on reading the proofs and preparing the illustrations. And in conclusion, I may express the wish that the present volume may be found as useful and acceptable to a numerous body of readers as I believe its predecessor has already proved itself.

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