150 PHILOSOPHICAL TRANSACTIONS. [ANNO 179/. 



apothecary's grains, 104.8 of which make 1000 grains Troy. But the weights 

 used were reduced to pounds avoirdupois. The measures of length were all taken 

 in English feet and inches. The experiments were all made in the open air, in the 

 court-yard of the arsenal at Munich; and they were all made in fair weather, and 

 between the hours of 9 and 12 in the forenoon, and 2 and 5 in the afternoon; but 

 the barrel was always charged, and the extremity of the bore closed by a leather 

 stopper, in the room where the powder was weighed. In placing the barrel on the 

 block of stone, great care was taken to put it exactly under the centre of gravity 

 of the weight employed to confine the generated elastic vapour. On applying the 

 red-hot ball to the vent tube, and fixing it in its place by its lever which supported 

 it, the explosion very soon followed. 



When the force of the generated elastic vapour was sufficient to raise the weight, 

 the explosion was attended by a very sharp and surprizingly loud report; but when 

 the weight was not raised, as also when it was only a little moved, but not suffi- 

 ciently to permit the leather stopper to be driven quite out of the bore, and the 

 elastic fluid to make its escape, the report was scarcely audible at the distance of a 

 few paces, and did not at all resemble the report which commonly attends the ex- 

 plosion of gunpowder. It was more like the noise which attends the breaking of 

 a small glass tube than any thing else to which I can compare it. In many of the 

 experiments in which the elastic vapour was confined, this feeble report attending 

 the explosion of the powder was immediately followed by another noise, totally 

 different from it, which appeared to be occasioned by the falling of the weight on 

 the end of the barrel, after it had been a little raised, but not sufficiently to permit 

 the leather stopper to be driven quite out of the bore. In some of these experi- 

 ments, a verysmall part only of the generated elastic fluid made its escape: in these 

 cases the report was of a particular kind, and though perfectly audible at some consi- 

 derable distance, yet not at all resembling the report of a musket. It was rather a very 

 strong, sudden hissing, than a clear, distinct, and sharp report. Though it could be 

 determined with the utmost certainty by the report of the explosion, whether any part 

 of the generated elasticfluidhad made its escape, yet for still greater precaution, a light 

 collar of very clean cotton wool was placed round the edge of the steel hemisphere, 

 where it rested on the end of the barrel, which could not fail to indicate by the black 

 colour it acquired, the escape of the elastic fluid, whenever it was strong enough 

 to raise the weight by which it was confined sufficiently to force its way out of the 

 barrel. After using a great variety of expedients, the best and most convenient 

 method of closing the end of the bore, and defending the flat surface of the steel 

 hemisphere from the corroding vapours, was found to be this: first, to cover the 

 end of the bore with a circular plate of thin oiled leather; then to lay on this a 

 very thin circular plate of hammered brass; and on this brass plate the flat surface 

 of the hemisphere. When the elastic fluid made its escape, a part of the leather 

 was constantly found to have been torn away, but never in more places than onej 

 viz. always on one side only. 



