l60 PHILOSOPHICAL TRANSACTIONS. [ANNO 17 Q7' 



following table in pounds avoirdupois ; but in order that a clearer and more perfect 

 idea may be formed of the real force of its elastic fluid, I have added a column in 

 which its force, answering to each charge of powder, is expressed in atmospheres. 

 The numbers in this column were computed in the following manner. The dia- 

 meter of the bore of the barrel at its muzzle being just ^ of an inch, the 

 area of its transverse section is 0.049088 of a superficial inch ; and assuming 

 the mean pressure of the atmosphere on 1 superficial inch equal to 1 5lbs. avoir- 

 dupois, this will give 0.73631 of a pound avoirdupois for that pressure on O.O49O88 

 of a superficial inch, or on a surface equal to the area by which the generated elas- 

 tic fluid acted on the weight employed to confine it ; consequently the weight ex- 

 pressed in pounds avoirdupois, which measured the force of the generated elastic 

 fluid in any given experiment, being divided by 0.73631, will show how many times 

 the pressure exerted by the fluid was greater than the mean pressure of the atmos- 

 phere. Thus in the experiment, No. 6. where the weight which measured the 

 elastic force of the generated fluid was = 504.8 lbs. avoirdupois, it is 504.8 -f-. 07 363 1 

 = 685.6 atmospheres. And so of the rest. 



I have said that the diameter of the bore of the barrel, used in the following 

 experiments, was just ± of an inch at its muzzle, and this is strictly true, as I 

 found on measuring it with the greatest care ; but its diameter is not perfectly the 

 same throughout its whole length, being rather narrower towards its lower end : 

 yet the capacity of the barrel being known, and also the diameter of the bore of 

 its muzzle, any small inequalities of the bore in any other part can in no wise 

 affect the result of the experiments, as will be evident to those who will take the 

 trouble to consider the matter for a moment with attention. I should not indeed 

 have thought it necessary to mention this circumstance, had I not been afraid that 

 some one who should calculate the joint capacities of the bore and of the vent 

 tube from their lengths and diameters, finding their calculation not to agree with 

 my determination of those capacities, as ascertained by filling them with mercury, 

 might suspect me of having committed an error. The mean diameter of the bore 

 of the barrel, as determined from its length and its capacity, turns out to be just 

 0.2281 of an inch ; the diameter of the vent tube being taken equal to 0.07 of an 

 inch, and its length 1.715 inch. 



