222 Means of measuring the initial Velocity 



a sufficient distance from the first disk, that the motion 

 given to the air by the explosion of the powder should not 

 hurt the motion of that disk. 



An apparatus exactly similar to the above was established 

 by colonel Grobert in a place belonging to the School of 

 Bridges and Causeways, where, with the commissioners, 

 he made, a few years ago, a great number of experiments, 

 at which were present several officers of the engineers and 

 artillery, among whom were general Marescot and the se- 

 nator La Martifiicre. 



This apparatus was far from having those di,mensions and 

 that perfection of which it was susceptible, and which the 

 author proposes to give it. The object of the commis- 

 sionersj therefore, was not so much to furnish results useful 

 to the artillery, as to ascertain what advantage might be de- 

 rived from it when constructed as it ought to be. 



It is proper, before we speak of our experiments, tliat we 

 should resolve a difficulty which naiurally occurs to all men 

 who are in the least acquainted with this subject, and which 

 arises from the enormous difference supposed to exist be- 

 tween the velocity of a projectile thrown from a cannon 

 and the angular velocity that may be given to the disks. 

 It is concluded, indeed, from the experiments already 

 known in regard to artillery, that the time employed by 

 the ball or bullet in passing over the distance of three or 

 four metres between the disks must be smaller than the 

 hundredth part of a second, and it can hardly be conceived 

 that during so short a time the disks can describe a sensible 

 arc. 



The solution of this difficulty is as follows: — When the 

 motion has become uniform, the wheel and axis make ge- 

 nerally 0-833 turns per second, and the axis of the disks 

 7*873 turns, which thus made 6-56 turns per second, cor- 

 respond to each turn of that wheel : therefore a point placed 

 on one disk at the distance of a metre from the axis passed 

 over about 41 metres per second, which gives for 1-lOOdth 

 second 41 centimetres, a length more than sufficient to 

 furnish very exact measures. 



The experin)ents were made with a common infantry 

 musket and a horse musketoon, the barrels of which were 

 resspectively 1-137 metre and 0-763 of interior length. 

 They were charged with cartridges furnished from the arse- 

 nal. The first series of experiments having been more re- 

 gular than was presumed, they were encouraged to employ 

 more precision in the charges and more care in the proofs. 

 I'he balls were weighed exactly ; their mean weight was 



24' 7 grammes. 



