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



this paper Mr. Hodgkinson acknowledges his deep obliga- 

 tions to the liberality of his friend Mr. Fairbairn, in pro- 

 curing for him the beams whereon to experiment. 



The contributions of Prof. Hodgkinson to the " Reports " 

 and ^^ Sections '^ of the British Association were nume- 

 rous and important. In proof of this it is only necessary 

 to refer to the opening address of the President, Professor 

 Sedgwick, at the Meeting at Edinburgh in 1834: — "The 

 Association may claim some credit for having brought into 

 general notice the ingenious investigations of Mr. Hodg- 

 kinson of Manchester.'^ 



In the Report of 1833 there are two papers by Mr. 

 Hodgkinson — 



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

 2nd, " 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 imperfectly 

 elastic bodies. After alluding to Newton's labours, as 

 recorded in the ' Principia,' Mr. Hodgkinson proceeds to 

 describe the methods by which his experiments were 

 made, and derives from them the following conclu- 

 sions : — 



1. All rigid bodies are possessed of some degree of elas- 

 ticity, and among bodies of the same nature the hardest are 

 generally the most elastic. 



2. There are no perfectly hard inelastic bodies, as as- 

 sumed by the early and some of the modem writers on 

 mechanics. 



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

 divided by the velocity of impact, is a ratio which (though 

 it decreases as the velocity increases) is nearly constant 

 when the same rigid bodies are struck together with con- 

 siderably different velocities. 



4. The elasticity, as defined in (3), is the same whether 

 the impinging bodies be great or small. 



