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



which he published in his ' Analytical Statics ' in 



1833*- 



The first series of experiments in this paper show that, 

 in cast iron, the extensions and compressions from equal 

 forces are nearly equal. Tredgold asserted that the same 

 force which destroyed the elasticity of a body by tension 

 would destroy it by compression. The next two experi- 

 ments disprove this assertion, and show that the resistance 

 to compression in cast iron is greater than to extension. 

 This discovery is important, and modified considerably the 

 best- constructed cast-iron beams of this period. The suc- 

 ceeding experiments, which are many and carefully re- 

 corded, were devised for the purpose of extending the con- 

 sequences of this practical discovery. And I shall here 

 avail myself of the Rev. Canon Moseley^s concise and 

 able exposition of the experiments and reasonings of Mr. 

 Hodgkinson by which he established the best form of cast- 

 iron beam. 



" Since the extension and the compression of the ma- 

 terial are the greatest at those points which are most dis- 

 tant from the neutral axis of the section, it is evident that, 

 the material cannot be in the state bordering upon rupture 

 at every point of the section at the same instant, unless 

 all the material of the compressed side be collected at the 

 same distance from the neutral axis, and likewise all the 

 material of the extended side, or unless the material of the 

 extended side and the material of the compressed side be 

 respectively collected into two geometrical lines parallel to 

 the neutral axis — a distribution manifestly impossible, since 

 it would produce an entire separation of the two sides of 

 the beam. 



" The nearest practicable approach to this form of section 



^ I hare Dr. Whewell's authority, in a letter which I received from him 

 a few day;? ago, in stating that he had not seen Mr. Hodgkinson's paper 

 when he wrote his ' Mechanics ' of 1824. 



