114 



ON THE POWER OF FLUIDS IN MOTION TO PRODUCE, 



FCff.l. 



any investigations that bear directly on the subject in question. My own re- 

 marks v/ere drawn up immediately after the publication of the memoir above 

 noticed, but were laid by and neglected until my attention was again drawn 

 towards them by an instance of the great effect of such pressures that fell un- 

 der my notice a few months since. I had occasion to trace the laws of sound 



propagated through water, and with tho view 

 of readily discharging a pistol at various depths 

 below the surface, contrived the apparatus in 

 Fig. 1. I had directed the box to be formed 

 of cast iron, but the maker, providing a strong 

 support for the breech of the pistol, and meet- 

 ing with delay in the casting, persuaded him- 

 self that thick tin plate, strengthened with 

 ribs, would give abundant strength to the re- 

 maining sides of the box. A covering of sheet 

 brass, an eighth of an inch thick, was subse- 

 quently added, and yet such is the nature of the action in question, that farther 

 security was necessary before this little case, which did not exceed eight inches 

 by five, could resist the powerful strains that tended to burst it inward when 

 exposed to the action of an ordinary pistol, exploded at a depth of five or six 

 feet below water. 



This additional instance of the occurrence of those destructive and appa- 

 rently paradoxical strains that had attracted the attention of the eminent che- 

 mist above mentioned, induced me to re-examine the paper I formerly showed 

 to you,* and to make public, with some slight addition, the results it contained. 

 I had shown, in a former paper, that many problems which appear purely 

 questions of statics, cannot be resolved without employing the elementary mo- 

 tions which connect such problems with those of dynamics. f The problem 

 before us is one of this class, and, when treated practically, is most conveni- 

 ently arranged as a question of statical pressures. 



Practical mechanics and engineers are accustomed to view the forces with 

 which they have to deal, under the twofold division of the loads which their 

 ..engines or structures bear, and the strains such loads occasion. 



* This paper was addressed to Dr. Patterson. 



t On the pressures produced by a heavy body when sustained by more than three supports. 

 Read before the R. Society of London, 1819. An. Philos., April, 1819.. 



