22 ANNUAL OF SCIENTIFIC DISCOVERY. 



' ' In wrought-iron bars no very perceptible effect was produced by 

 10,000 successive deflections by means of a revolving cam, each deflec- 

 tion being due to half the weight which, when applied statically, pro- 

 duced a large permanent flexure. 



" Under the second head, namely, the inquiry into the mechanical 

 effects of percussions and moving weights, a great number of experi- 

 ments have been made to illustrate the impact of heavy bodies on 

 beams. From these it appears that bars of cast-iron of the same 

 length and weight, struck horizontally by the same ball (by means of 

 the apparatus above described for long continued impact),- offer the 

 same resistance to impact, whatever be the form of their transverse sec- 

 tion, provided the sectional area be the same. Thus, a bar six by one 

 and a half inches in ssction", placed on supports about fourteen feet 

 asunder, required the same magnitude of blow to break it in the 

 middle, whether it was struck on the broad side or the narrow one, 

 and similar blows were required to break a bar of the same length, 

 the section of which was a square of three inches, and therefore of the 

 same sectional area and weight as the first. Another course of experi- 

 ments tried with the same apparatus showed, amongst other results, 

 that the deflections of wrought-iron bars produced by the striking ball 

 were nearly as the velocity of impact. The deflections in cast-iron are 

 greater than in proportion to ths velocity. 



" A set of experiments was undertaken to obtain the effects of addi- 

 tional loads spread uniformly over a beam, increasing its power of 

 bearing impacts from the sams ball falling perpendicularly upon it. 

 It was found that beams of cast-iron, loaded to a certain degree with 

 weights spread over their whole length, and so attached to them as 

 not to prevent the flexure of the bav, resisted greater impacts from the 

 same body falling on them than when the beams were unloaded, in 

 the ratio of two to one. The bars in this cass were struck in the mid- 

 dle by the same ball falling vertically, through different heights, and 

 the deflections were nearly as the velocity of impact. 



" We have also carried on a series of experiments to compare the 

 mechanical effect produced by weights passing with more or less ve- 

 locity, over bridges, with their effect when placed at rest upon them. 

 For this purpose, amongst other mathods, an apparatus was construct- 

 ed, by means of which a car, loaded at pleasure with various weights, 

 was allowed to run down an inclined plane. The iron bars which 

 were the subject of the experiment were fixed horizontally at the 

 bottom of the plane, in such a manner that the loaded car would pass 

 over them with the velocity acquired in its descent. Thus the effects 

 of giving different velocities to the loaded car, in depressing or frac- 

 turing the bars, could be observed and compared with the effects of the 

 same loads placed at rest upon the bar. A great number of experi- 

 ments were tried with this apparatus for ths purpose of comparing 

 the effects of different loads and velocities upon bars of various dimen- 

 sions, and the general result obtained was, that the deflection pro- 

 duced by a load passing along the bar was greater than that which 

 was produced by placing the same load at rest upon the middle of the 

 bar, and that, this deflection was increased when the velocity was in- 



