VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 155 



totally unexpected by me. It was a new lesson to teach me caution in these danger- 

 ous pursuits. 



Before giving an account of my subsequent experiments on this subject, I shall 

 stop here for a moment to make an estimate, from the known strength of iron, and 

 the area of the fracture of the barrel, of the real force employed by the elastic va- 

 pour to burst it. In a course of experiments on the strength of various bodies 

 which I began many years ago, and an account of which I intend at some future 

 period to lay before the r. s.,* I found, by taking the mean of the results of several 

 experiments, that a cylinder of good tough hammered iron, the area of whose 

 transverse section was only , 6 9 00 of an inch, was able to sustain a weight of 1 19 lbs. 

 avoirdupois, without breaking. This gives 63466 lbs. for the weight which a 

 cylinder of the same iron whose transverse section is 1 inch, would be able to sus- 

 tain without being broken. The area of the fracture of the barrel before men- 

 tioned was measured with the greatest care, and was found to measure very exactly ' 

 6-1- superficial inches. If now we suppose the iron of which this barrel was formed, 

 to be as strong as that whose strength I determined, and I have no reason to sus- 

 pect it to be of an inferior quality, in that case, the force actually employed in 

 bursting the barrel must have been equal to the pressure of a weight of 4 12529 lbs. 

 For the resistance or cohesion of 1 inch, is to 63466 lbs. as that of 6^- inches to 

 412529 lbs. ; and this force, so astonishingly great, was exerted by a body which 

 weighed less than 26 grs. Troy, and which acted in a space that hardly amounted 

 to -jig- of a cubic inch. 



To compare this force exerted by the elastic vapour generated in the combustion 

 of gunpowder, and by which the barrel was burst, to the pressure of the atmos- 

 phere, it is necessary to determine the area of a longitudinal section of the bore of 

 the piece. Now the diameter of the bore being 4- of an inch, and its length (after 

 deducting 0.15 of an inch for the length of the leathern stoppers) 2 inches, the 

 area of its longitudinal section turns out to have been -i- an inch. And if now we 

 assume the mean pressure of the atmosphere =15 lbs. avoirdupois for each super- 

 ficial inch, this will give 7-1- for that on a surface = 4- inch, equal to the area of a 

 longitudinal section of the bore of the barrel. But we have just found that the 

 force actually exerted by the elastic vapour in bursting the barrel, amounted to 

 412529 lbs. ; this force was therefore 55004 times greater than the mean pressure 



* Since writing the above, I have met with a misfortune which has put it out of my power to fulfil 

 my promise to the r. s. On my return to England from Germany in October, 1795, after an absence 

 of 1 1 years, I was stopped in my post-chaise in St. Paul's church-yard, in London, at six o'clock in the 

 evening, and robbed of a trunk which was behind my carriage, containing all my private papers and my 

 original notes and observations on philosophical subjects. By this cruel accident I have been deprived 

 of the fruits of the labours of my whole life j and have lost all that I held most valuable. This most 

 severe blow has left an impression on my mind, which I feel that nothing will ever be able entirely to 

 remove. — Orig. 



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