MEMOIR OF EATOX HODGKIXSON". 215 



The Rev. Canon Moselcy further observes on this point, " It is only in cast- 

 iron beams that it is customary to seek an economy of the material in the stroim'th 

 of the section of the beam ; the same principle of cconcjmy is surely, however, 

 ap]ilicable to beams of wood." 



Tliis victory over the material foe is entirely Mr. Iloflgkiiison's own ; and, 

 using- tlie languag'e of the president of the British Association at Manchester, 

 1861, there is no one to divide the honor of this useful achievement with him. 

 The Hodgkinson beam is really what its name would imply, as he originated the 

 conception and pursued it with judgment and industry until the best form of 

 beam was fully determined. This beam has been the pole star for engineers 

 and builders during the last 20 years, a period in which construction of all kinds 

 has been in great demand, and in which the ingenuity and skill of the constructor 

 has been confronted with many and formidable difficulties. Railways, ship- 

 building, and public works of various kinds have opened out new channels for 

 the application of cast and wrought iron ; and when this material is placed in 

 new and untried positions, it is no little point which is gained when its tensile 

 and crushing strength is determined, and the best form investigated by which 

 the safety of large structures is secured. This was the life-work of Professor 

 Hodgkinson. 



It is a great thing, which no man of science lightly appreciates in these days 

 of mental activity, for a man to point to a useful discover}^ and claim it as his 

 own without a rival, to say to himself, (his own precious reward.) " 1 drew it 

 foi'th from the dark chaos in which it had been entombed for ages to the light 

 of day, and now I leave it as a legacy to my countrymen, trusting that the chance 

 of calamities such as that which happened at Hartley Colliery, where 200 men 

 lost their lives by the breaking of a cast-iron beam, may be diminished, if not 

 entirely obviated." In this paper Jlr. Hodgkinson acknowledges his deep 

 obligations to the liberality of his friend Mr. Fairbairn, in procuring for him the 

 beaTHS whereon to experiment. 



The (Contributions of Professor Hodgkinson to the " Reports" and " Sections" 

 of the British Association were numerous and important. In proof of this it is 

 only necessary to refer to the opening address of the president, Professor Sedg- 

 wick, at the meeting at Edinburgh in 1834 : " The association may claim some 

 credit for having brought into general notice the ingenious investigations of Mr. 

 Hodgkinson of Manchester." 



In the Report of 1833 there are two papers by Mr, Hodgkinson: 



1. '^ On the Effect of Impact of Beams." 



2. " On the Direct Strength of Cast Iron." 



In the Report of the British Association of 1834, we find an extended inquiry 

 into the collision of imperlectly elastic bodies. After alluding to Newton's labors, 

 as recorded in the ♦' Principia,'^ Mr. Hodgkinson proceeds to describe the methods 

 by which his exi)eriments were made, and derives from them the following non- 

 elusions : 



1. All rigid bodies are possessed of some degree of elasticity, and among 

 bodies of the same nature the hardest are generally the most elastic. 



2. There are no perfectly hard inelastic bodies, as assumed by the early and 

 some of the modern waiters on mechanics. 



3. The elasticity, as measured by the velocity of recoil divided by the velocity 

 of imi)act, is a ratio which (though it decreases as the velocity increases) is 

 nearly constant when the same rigid bcxlies are struck together with considerably 

 different velocities. 



4. The elasticity, as defined in 3, is the same whether the impinging bodies 

 be great or small. 



5. The elasticity is the same, whatever be the relative weights of the imj)ing- 

 ing bodies. 



6. On impacts between bodies differing very nmcli in hardness, the elasticity 

 with which they separate is nearly that of the softer body. 



