14.2 Sir C. Fox on the size of Pins connecting Flat Links [Mar. 30, 



insufficient ; and accordingly a few experimental links were prepared with 

 their heads 2 inches wider than before (as shown in fig. 4) ; but these never- 

 theless were found to require no additional force to tear asunder ; hence it 

 became obvious that fracture arose from some cause not yet ascertained. 



As has already been stated, the rupture took place across the widest 

 part of the head (C C, fig. 2) ; but on attempting to adjust the piece broken 

 off to the position it originally occupied in the link, it was observed that, 

 while the fractured surfaces came in contact at the outside of the head, 

 they were a considerable distance apart at the edge of the pin-hole (see 

 fig. 2). 



This at once proved that during the application of the tension, which 

 at last ended in producing fracture, the various portions of the head had 

 been subject to very unequal strains ; and upon careful examination, the 

 rationale of this fracture became apparent from the consideration that the 

 hole, which originally was round, had become pear-shaped (see fig. 2), 

 having altered its position, and that the iron of the link which, during the 

 application of the load, bore upon the pin, and was consequently in a state 

 of compression, had become considerably thickened in consequence, as was 

 now evident, of an effort to obtain a greater bearing surface (see A, figs. 

 2 & 3), while the other portion of the iron around the pinhole, being sub- 

 ject to tension, had been so weakened and thinned by being stretched, as 

 to cause a tearing action to take place, which, having once commenced, 

 would obviously, by the continuance of the same strain, rend through the 

 entire head, no matter what its width might be. 



From this it was clear that any increase of size in the head (unless by 

 thickening, which, as I have before stated, is inadmissible) was of no avail ; 

 and it was now that the principle which forms the subject of this paper 

 became manifest viz., that there was a certain area of the semicylin- 

 drical surface of the hole having a bearing on the pin proportionate to 

 the transverse section of the body or narrowest part of a link, and quite 

 essential to its having equal strength in all its parts ; and that any de- 

 parture from this proportion could not fail to bring about either waste of 

 iron in the body of the links, if the pin were of insufficient size to offer 

 proper bearing surface, or waste of metal in the heads of the links and in 

 the pins, if the latter were larger than necessary for obtaining this fixed 

 proportion of areas. 



Having arrived at this point, a link, similar in all respects to the pre- 

 vious one, with holes 4| inches in diameter, and which broke across the 

 head with 180 tons, was taken, and its holes enlarged to 6 inches, but with- 

 out increasing the width of the head, which still remained 16^ inches ; so 

 that the only difference was the removal of an annular piece | inch in width 

 from the hole, and so making it 6 inches instead of 4| inches in diameter, 

 thereby actually diminishing the quantity of iron in the head to this extent 

 when it was most interesting to discover that by this slight alteration, by 

 which the semicylindrical surface bearing on the pin had been increased 



