868 
ME. HODGKmSON’S EXPEEDIEXTAL EESEAECHES 
Second London Mixture. 
Centre, 35‘02 tons. Intermediate part, 42’56 tons. 
Second London Mixture. — Specimens cut from pillars 1^ inch, diameter. 
Centre, 46‘46 tons. Intermediate part, 49'59 tons. 
By comparing the results of the experiments on the resisting powers of the different 
irons in the kingdom to a crushing force, with those obtained from the direct strengths 
of pillars of the same irons, 10 feet long and 2^ inches diameter, it appears that the 
crushing force varies rather widely from beiug as the direct strength of pillars from the 
same model. Though the ratio assumed is merely an approximation, it will afford 
means of approaching to the falling off in the strength of pillars, when the resistance of 
the different parts to a crushing force is known. 
Taking the results from the breaking weights of three of the strongest hon pillars, 
each 10 feet long and 2J inches diameter, and the crushing weights of the hons from 
those pillars, we have from the strongest pillars-— 
>-Mean 63342 lbs. 
Breaking weights of the pillars. 
660861 
62794 
61147. 
and from those of the weakest irons — 
626801 
49387 [Mean 48996 lbs. 
449184 
Crushing weights of the iron in their sections. 
4373601 
486760 [Mean 464070 lbs. 
4691104 
3384601 
346130 [Mean 319346 lbs. 
273466J 
Comparing the breaking weights of the pillars with the crushing weights of the irons, 
48996 : 63342 : : 319346 : 412867. 
The last number, 412867, ought to have been 464070 if the breaking weights had 
been as the crushing weights. But the breaking weight of pillars depends on the tensile 
and crushing weights conjointly, though principally upon the latter ; the assumption of 
that proportion must be taken as an approximation only, as pre^dously mentioned. 
Let r, r' be the resistances to crushing per square inch of the parts near to the chcum- 
ference and to the centre respectively; D, d the external diameter, and that which 
includes the softer part of the metal near to the centre. Then r — /= the falling off 
per square inch in the resistance of the softer part below that of the external paid. 
Whence —^= the defect of resistance of the central part, the resistance of the external 
part being represented by unity. 
If then w be the breaking weight of a pillar ; m, n constants, and as before assumed’ 
for solid pillars of uniform texture, 
w=mJT, 
(A.) 
