321 



in feet, and m a weight which varied from 49' 94 tons in the strongest 

 iron we tried, to 33' 60 tons in the weakest. 



The ultimate decrement of length, in pillars of various lengths but 

 of the same diameter, varies inversely as the length nearly. Thus 

 the ultimate decrements of pillars 10 feet, 7 feet 6 inches, 6 feet 

 3 inches, and 5 feet, vary as 2, 3, 3 and 4 nearly, according to the 

 experiments, from which it appeared that the mean decrement of 

 a 10-feet pillar was -176 inch. 



Irregularity in Cast Iron. 



The formulae arrived at in this paper are on the supposition that 

 the iron of which the pillars are composed is uniform throughout the 

 whole section in every part ; but this was not strictly the case in any 

 of the solid pillars experimented upon. They were always found to 

 be softer in the centre than in other parts. To ascertain the 

 difference of strength in the sections of the pillars used, small cylin- 

 ders | inch diameter and 1| inch high, were cut from the centre, and 

 from the part between the centre and the circumference, and there 

 was always found to be a difference in the crushing strength of the 

 metal from the two parts, amounting perhaps to about one-sixth. 

 The thin rings of hollow cylinders resisted in a much higher degree 

 than the iron from solid cylinders. As an example, the central part 

 of a solid cylinder of Low Moor iron No. 2, was crushed with 29 '65 

 tons per square inch, and the part nearer to the circumference re- 

 quired 34 '5 9 tons per square inch ; cylinders out of a thin shell half 

 an inch thick, of the same iron, required 39*06 tons per square inch ; 

 and other cylinders from still thinner shells of the same metal, re- 

 quired 50 tons per square inch, or upwards, to crush them. 



As these variations in cast iron have been little inquired into, ex- 

 cept by myself, and have never, so far as I know, been subjected 

 to computation, I have bestowed considerable trouble upon the 

 matter, in an experimental point of view, and endeavoured to intro- 

 duce into the formulee previously given, changes which will in some 

 degree include the irregularities observed. 



