As collateral testimony to the important effects of vibration may be mentioned:— A comparison of the coefficients of friction during motion and those at the commencement of movement or of repose. The existence of a nearly vertical face generally assumed, when unshaken by artificial means, in the bared top earth in a quarry, shallow well, gravel or sand pit, pond, and even a river-bank or a cliff, which experience has proved could not be maintained when subject to vibration. The fact that timber piles, which are chiefly supported by the frictional resistance of their surfaces, will not sustain a rolling, _i.e._, a vibratory, load equal to that of a fixed load, and also that the method of driving in soils easily disturbed, such as sand, is also considered as reducing the safe load according to the percussive action and frequent vibration caused by a pile-driver, whether worked by steam, hand, or by means of an explosive substance. As further proof may be named that in pile-driving, especially in open soil, piles continually driven penetrate the earth considerably quicker and easier than if driven at intervals, as the latter system allows the soil to settle round them and the loosening and friction destroying effects of vibration are lessened. The experiments made by Mr. J. A. Longridge, M. Inst. C.E., for Mr. G. R. Stephenson, Past-President Inst. C.E., in Morecambe Bay, England, showed that by vibration the bearing power of driven timber piles was reduced to one-fourth or one-fifth of that when subject to a steady non-vibratory load. Its deleterious effect on the structure of such a solid substance as iron, &c., particularly when it is loaded beyond its elastic limit. It is generally agreed that a substance is broken sooner when a load is intermittingly imposed than when the same load is permanently placed upon a structure. The experiments of Professor Stokes, 1849; M. Phillips, 1855; M. Renaudot, 1861; M. Bresse, 1866; and recently of Dr. Winkler and others, show that the increase of the intensity of strain consequent upon the dynamic effect of a suddenly-applied moving load may be as much as 33 per cent. more than that of the computed statical pressure. The fact that in masonry piers of considerable height and small dimensions, as in piers of viaducts, the vibration caused by trains loosens the brickwork or masonry and necessitates frequent repairs.