262 L iterary and Philosophical Society. 



an enterprise which will represent the engineering skill of 

 the present time, and will be the admiration of future ages. 

 E. Clark, Esq., who superintended the building of the 

 tubular bridges, speaks in the highest terms of Mr. Hodg- 

 kinson's labours in fixing the proper dimensions of the 

 bridges. 



' We are indebted to him also for nearly the whole of 

 the mathematical calculations in reducing the experiments 

 which were made into a form fit for application to a large 

 structure. But we are also indebted to Mr. Fairbairn for 

 a great portion of the practical construction of the bridges. 



' The answers given by Mr. Hodgkinson to his inquiries, 

 and which rendered such signal service to the engineer in 

 the execution of his novel design, are as follows : — 



* I. The value of (/*) the strain upon a square inch at 

 the top or bottom of the tube is constant in material of the 

 same nature, while it varies from 19, 14, to 7| tons when 

 the thickness of metal varies from "525, '272, to '124 of an 

 inch. The determination of (/) is the chief obstacle to 

 obtaining a formula for the computation of the strength of 

 tubes of every form. 



* The strength of the Conway tube was calculated to 

 bear 1,084 tons when the value of (/) was taken at 8 tons 

 and the deflection about 15^ inches in the middle. 



* 2. The strength of similar tubes was somewhat lower 

 than the square of their linear dimensions, being about i -9 

 power instead of the square. 



* 3. The tubes may be reduced in strength and thickness 

 towards the ends corresponding to the ratio indicated by 

 theory, viz. that the strain at any point of the tube is 

 proportional to the rectangle of the two parts into which 

 that point divides the length of the tube, 



