When we consider to what extent pillars of iron and of timber are used for the support of building's, and reflect that there are no satisfactory rules by which to measure the strength of pillars, it becomes a matter of great importance to obtain such rules by means of experiment, and, if possible, to discover the laws on which they are founded. A feeling of this kind, heightened by the remarks of Dr. Robison, in his Mechanical Philosophy, and by the strongly-expressed opinion as to our want of such knowledge by Mr. Barlow, led me to wish to undertake the inquiry. I mentioned the matter, therefore, to my friend Mr. Fairrairn, who, with that liberality which I have experienced from him on former occasions, at once put every means of a full investigation into my hands. He expressed a wish that I should extend the inquiry to pillars of various kinds, ancient as well as modern; and leave no part of the subject in uncertainty for want of experiments sufficiently varied and extensive. Thus freed from restraint, I endeavoured, in my wish to acquire the requisite information, to forget the expense to which I put my friend, and have made every effort to render the experiments at least ample, correct, and useful. The pillars on which the experiments were made, were mostly of cast iron, as being the material in most general use; but some were of wrought iron and steel, and others of wood. In the earlier experiments, the pillars used were uniform cylinders, either with their ends rounded, so that the crushing force might pass through the axis, or with flat and parallel ends, so that the pillar, when placed between two perfectly parallel crushing surfaces, might have its ends completely bedded against them.