122 Mr. Rennie's account of experime?ils 
the fourth power of the radius, in observing the relations of 
theory and practice to accord with each other. This was 
admitted by Euler in his memoir of 1780, in his elaborate 
investigation of the forms of columns. Mr. Coulomb had 
however shown before that time, how inapplicable all these 
calculations were to columns under common circumstances; 
and you, Sir, have repeated the observation in your lectures 
on natural philosophy. The results of experiments have also 
been equally discordant; since it is deduced from those of 
Reynolds, that the power required to crush a cubic quarter 
of an inch of cast iron, is 44,8ooolbs. avoirdupoise, or 200 tons ; 
whereas by the average of thirteen experiments made by me 
on cubes of the same size, the amount never exceeded 
10392. 53lbs, not quite five tons.* This may be seen by 
referring to the tables. There were four kinds of iron used, 
viz. 1st. iron taken from the centre of a large block, whose 
crystals were similar in appearance and magnitude to those 
evinced in the fracture of what is usually termed gun metal. 
2ndly. Iron taken from a small easting, close grained, and of a 
dull grey colour. 3rdly. Iron cast horizontally in bars of Jth 
inches square, 8 inches long. ^thly. Iron cast vertically, same 
size as last. These castings were reduced equally on every 
side to of an inch square : thus removing the hard external 
coat usually surrounding metal castings. They were all 
subjected to a gauge. The bars were then presumed to be 
* It is probable that Mr. Reynolds made his experiments on metal cast at the 
furnace of Maidley Wood, which is of a very strong and superior quality ; but this 
circumstance can have been but of little importance compared to the great dispro^ 
portion of the results. 
