OF IRON BEAMS. 409 



having less to support in its own weight. It 

 may be stated in illusti-ation of this remark, 

 that there are usually upwards of 100 tons of 

 metal in the beams supporting the floors of 

 a factory. 



3. To attain these objects as far as lay in the 

 power of the author of this paper, a number 

 of experiments have been made; but before 

 giving an account of them, it may be proper to 

 describe the nature of the strain to which bodies 

 thus acted upon are exposed. 



This subject, I conceive, has not been well 

 understood ; but I indulge a hope that the 

 theory I gave, in a paper on the Strength of 

 Materials in the 4th vol., New Series, of the 

 Manchester Memoirs, is both general and 

 correct. It is in agreement with that of Dr. 

 Robison, and of Coulomb, properly considered, so 

 far as they have gone -, and the following abstract 

 is in pursuance of it. 



4. Suppose a beam, placed horizontal, with 

 one end firmly fixed in a wall and a weight hung 

 at the other, it will bend : but, it is evident, that 

 could not take place, except by the lengthening 

 of the top parts, or the compression of the 

 bottom, or by both. Now both of these actu- 



3 r 



