190 MEMOIR OF THE LATE PROF. E. HODGKINSON^ F.R.S. 



engineering science ; but there were other important re- 

 sults obtained by other Members of the Commission, to 

 which it may not be deemed out of place to refer. 



The experiments at Portsmouth Dockyard, conducted by 

 Colonel Sir Henry James, and the discussion of the results 

 by Prof. Willis and Prof. Stokes, were also the work of 

 the Commissioners. And it would be no easy task to over- 

 estimate the value of these labours, both on account of the 

 novel nature of the experiments and the mathematical 

 deductions to which they conducted when placed in the 

 hands of Prof. Stokes. 



Col. Sir Henry James and Capt. Galton subjected cast- 

 iron bars, placed between fixed supports, to 100,000 suc- 

 cessive deflections, at the rate of four per minute, by means 

 of a cam. When the deflections were one-third of the 

 ultimate deflection, the bars were not weakened ; when, 

 however, the deflections were one-half of the ultimate 

 deflection, the bars were broken with less than 900 de- 

 pressions. 



Prof. Hodgkinson subjected cast-iron bars, firmly fixed 

 between supports, to 4000 continued impacts. When 

 the blow was such as to deflect the bars one-third of their 

 ultimate deflection, they resisted the concussion of 4000 

 impacts without injury ; but when the blow was such as to 

 deflect the bars one-half of their ultimate deflection, no bar 

 could resist 4000 depressions. These results strikingly 

 confirm each other. 



Col. James and Capt. Galton caused a weight, equal to 

 one-half the breaking- weight of the cast-iron bar, to be 

 drawn backwards and forwards from one end of the bar to 

 the other. The bar was not weakened by 96,000 transits 

 of the weight. No perceptible effect was produced in 

 wrought-iron bars by 10,000 successive deflections, each of 

 which was equal to that produced by half the breaking- 

 weight. 



