VOL. LXXI.j PHILOSOPHICAL TRANSACTIONS. 107 



charge of powder may be half an ounce, and it should always be put up in a 

 cartridge of very fine paper ; and after the piece is loaded it should be primed 

 with other powder, first taking care to prick the cartridge by thrusting a priming 

 wire down the vent. The machine for the tape to slide through may be the 

 same as is described by Dr. Hutton in his account of his experiments on the 

 initial velocities of cannon balls; as his method is much better calculated to 

 answer the purpose than that proposed and made use of by Mr. Robins. It will 

 also be better for the axis of the pendulous rods to rest on level pieces of wood 

 or iron, than for them to move in circular grooves : only care must be taken to 

 confine them by staples or some other contrivance, to prevent their slipping 

 out of their places. The trunnions, by means of which the barrel is connected 

 with the pendulous rods, and on which it is supported, should be as small as 

 possible, in order to lessen the friction ; and for the same reason they should be 

 well polished, as well as the grooves that receive them. They need not be cast 

 on the barrel, but may be screwed into it after it is finished. 



In making the experiments, regard must be had to the heat of the barrel, as 

 well as to the temperature of the atmosphere ; for heat and cold, dryness and 

 moisture, have a very sensible effect on gunpowder to increase or diminish its 

 force. If therefore a very great degree of accuracy is at any time required, it 

 will be best to begin by firing the piece 2 or 3 times merely to warm it ; after 

 which 3 or 4 experiments may be made with standard powder, to determine anew 

 the proof mark, as the strength of the same powder is different on different 

 days ; and when this is done, the experiments with the powder that is to be 

 proved are to be made, taking care to preserve the same interval of time between 

 the firings, that the heat of the piece may be the same in each trial. If all 

 these precautions are taken, and if the bullets are of the same weight and di- 

 mensions, powder may be proved by this method with much greater accuracy 

 than has hitherto been done by any of the common methods made use of for 

 that purpose.* 



Of the comparative goodness, or value, of powder of different degrees of 

 strength. — Estimating the strength of powder by the square of the velocity a 

 given charge gives to a bullet, by experiment Mr. T. finds that double proof 

 Battle powder is stronger than the same weight of government powder, in the 

 proportion of 6 to 5. But as the former was sold at 2 shillings the lb. and the 



* The foregoing method for an eprouvette, appears to be the same as a new one hinted and recom- 

 mended by Mr. Robins, at p. 123 of his New Principles of Gunnery. And from the same remark 

 of Mr. Robins's also, Dr. Hutton made one with a small brass cannon, and several other improved 

 contrivances, which was much used at Woolwich, and found to be a very regular and accurate eprou- 

 vette, and most ready and convenient when used with powder only, without balls. 



p 2 



