182 MEMOIR OF THE LATE PROF. E. HODGKINSON, F.R.S. 



The above is but a basty and imperfect glance at this im- 

 portant paper, which appeared at the time when the rail- 

 way system was developing itself by means of the applica- 

 tion of cast- and wrought-iron pillars to the construction 

 of bridges, &c. No engineer who has in future to deal 

 with this subject must omit the reading of this paper. 



In the Philosophical Transactions for 1857, there is 

 another paper by Mr. Hodgkinson on the strength of 

 pillars. The object here is to confirm the conclusions of 

 the first paper by means of larger experiments, made by 

 an apparatus three times as great as the apparatus used on 

 the former occasion. Having been unsuccessful in finding 

 the weight producing incipient flexure, Mr. Hodgkinson 

 devoted his attention to finding the breaking- weight, the 

 deflection, and decrement of length produced by the weight 

 laid on the pillars. The pillars vdth both ends rounded 

 broke in one place, in the middle ; but the pillars with 

 both ends flat broke in three places, the middle, and at 

 each end. When one end was flat and the other rounded, 

 it broke at one-third the distance from the rounded end. 



The formulse in the former paper are here slightly cor- 

 rected, as being more in accordance with the results of 

 larger experiments. 



Thus, in pillars whose ends are flat and well bedded, the 

 formula becomes 



D3 5 — c??-5 



^ = 42-347 j^.-63 ^ 



instead of 



w— 46*65 



L^-7 



as given in the first paper. 



It is a matter of observation long recorded, both by Mr. 

 Hodgkinson and other experimentalists, that the metal in 

 large^ eastings is not uniform in density, the density dimin- 



