Mr Buchanan on tJie Strength, qf Materials. 150 
a few simple considerations, arrived at those remarkable laws of 
strength, which not only throw light on the economy of nature; 
but still afford, with the aid of experiment, the safest rules for 
calculating the strength of materials in the various cases which oc- 
cur in practice. While the direct strength of cohesion is propor- 
tional to the area of the section of fracture, Galileo shewed, 
that the transverse strength of any beam, must depend also on 
its lengtli and depth, being impaired by the one, and strengthen- 
ed by the other ; and this single fact includes the whole theory 
. of the transverse strain. His views regarding the internal me- 
. chanism of the bar, and the actions of the particles within the 
section of fracture are no doubt inaccurate, and succeeding 
^ philosophers have taken great pains to improve his theory in 
this respect. But this appears of little moment so long as the 
main fact remains uncontradicted, and is rather indeed demon- 
strated by ail our experience. Admit this, and a few accurate 
experiments are only wanting to adapt it to practice, — experi- 
ments on beams of different materials, of different forms of sec- 
tion, and under any other circumstances which may affect the 
results. The internal process of fracture, may no doubt be an 
object well worthy of philosophic inquiry, and the results which 
have been obtained on this point, by Mr Barlow of Woolwich, 
in his valuable essay on the strength of timber, are highly in- 
teresting and instructive. His demonstrations are clear and 
conclusive, and in the true spirit of geometry; while his ex- 
periments are simple, and well adapted both to illustrate and 
confirm his views. Still, however, these speculations appear ra- 
ther refined for practice. The internal structure of bodies is so 
various, that no general rule can be laid down. It is also so lit- 
tle known, and leads to such intricate considerations as tend 
greatly to embarrass the subject. It appears simpler, therefore, to 
throw this ‘element entirely out of the calculation, and to con- 
tent ourselves with the original law of Galileo, which has been 
since established by every succeeding observer. This brings 
the subject within a very small compass ; and comprehends 
in one rule of admirable simplicity, all the diversified cases 
which can occur in practice. What is wanting to give effect to this 
law, is a series of experiments made on so large a scale, and with 
such full and accurate means of observation, as would leave no 
