134 Experiments to determine 



But we have just found that the force actually exerted 

 by the elastic vapour in bursting the barrel, amounted 

 to 412,529 lbs.; this force was therefore 55,004 times 

 greater than the mean pressure of the atmosphere. For 

 it is as ^\ lbs. to i atmosphere, so 412,529 lbs. to 55,004 

 atmospheres. 



Thinking it might perhaps be more satisfactory to 

 know the real strength of the identical iron of which the 

 barrel used in the before-mentioned experiment was con- 

 structed, rather than to rest the determination of the 

 strength of the barrel upon the decision of the strength 

 of iron taken from another parcel, and which very pos- 

 sibly might be of a different quality, since writing the 

 above, I have taken the trouble to ascertain the strength 

 of the iron of which the barrel was made, which was 

 done in the following manner. Having the one half of 

 the barrel still in my possession, I caused small pieces, 

 1 inches long, and about \ of an inch square, to be cut 

 out of the solid block of metal, in the direction of its 

 length, with a fine saw ; and these pieces being first 

 made round in their middle by filing, and then by turn- 

 ing in a lathe with a very sharp instrument, were re- 

 duced to such a size as was necessary, in order to their 

 being pulled asunder in my machine for measuring the 

 strength of bodies. In this machine the body to be 

 pulled asunder is held fast by two strong vices, the one 

 fastened to the floor, and the other suspended to the 

 short arm of a Roman balance, or common steel-yard ; 

 and, in order that the bodies so suspended may not be 

 injured by the jaws of the vices, so as to be weakened 

 and to vitiate the experiments, they are not made 

 cylindrical, but they are made larger at their two ends 

 where they are held by the vices, and from thence their 



