CHAPTER VII

THE PIER BASE

§ 1. IN § 3 of Chap. III., it was stated that when a wall had to sustain an addition of vertical pressure, it was first fitted to sustain it by some addition to its own thickness; but if the pressure became very great, by being gathered up into PIERS.

I must first make the reader understand what I mean by a wall’s being gathered up. Take a piece of tolerably thick drawing-paper, or thin Bristol board, five or six inches square. Set it on its edge on the table, and put a small octavo book on the edge or top of it, and it will bend instantly. Tear it into four strips all across, and roll up each strip tightly. Set these rolls on end on the table, and they will carry the small octavo perfectly well. Now the thickness or substance of the paper employed to carry the weight is exactly the same as it was before, only it is differently arranged, that is to say, “gathered up.”* If, therefore, a wall be gathered up like the

* The experiment is not quite fair in this rude fashion; for the small rolls owe their increase of strength much more to their tubular form than their aggregation of material; but if the paper be cut up into small strips, and tied together firmly in three or four compact bundles, it will exhibit increase of strength enough to show the principle.¹ I could have wished, before writing this chapter, to have given more study to the difficult subject of the strength of shafts of different materials and structure; but I cannot enter into every inquiry which general criticism might suggest, and this I believe to be one which would have occupied the reader with less profit than many others: all that is necessary for him to note is, that the great increase of strength gained by a tubular form in iron shafts, of given solid contents, is no contradiction to the general principle stated in the text, that the strength of materials is most available when they are most concentrated. The strength of the tube is owing to certain properties of the arch formed by its sides, not

¹ [The rest of the note-“I could have wished ... sound of his voice”-was in ed. I printed as Appendix “16. Strength of Shafts”; and the note here continued “Vide, however, Appendix 16, “Strength of Shafts.”]

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[Version 0.04: March 2008]