228 Means of measuring the initial Velocity 



lated into French by colonel Villantroys, may be considereci 

 as the most complete and most instructive treatise on ba- 

 listic experiments that ever appeared. 



The apparatus proposed by colonel Grobert, as may be 

 seen, is very different from those employed by the authors 

 above mentioned ; and whatever merit may be due to expe- 

 riments made with pendulums, it must no doubt be allowed 

 that it may be of some utility to make new ones by a very 

 ingenious method, in which simplicity and oeconomy are 

 united, and which leads to the proposed end in the most 

 direct manner, as the velocities sought for are deduced 

 merely from the observation of the time employed by a 

 moving body to make a certain number of revolutions 

 around a fixed axis : an observation free from those dynamic 

 calculations which are required by the method of Robins. 



We have said nothing of the labours of Antoni in regard 

 to the object of this report, and yet we cannot omit men- 

 tioning a machine which he speaks of in his Essai sur la 

 Poudre, a French translation of which was published by 

 M. de Flavigni in 1773. This machine, which Antoni 

 says was invented by a mechanician named Mathey, consists 

 of a horizontal circle supported by its centre on the upper 

 extremity of a vertical axis, and serving as a base to a hollow 

 cylinder of paper. A rotary motion is given to this cy- 

 linder by means of a weight affixed to a cord which passes 

 over a pulley, and the projectile, thrown in a horizontal di- 

 rection, when the angular velocity has become constant in 

 the vertical plane of that axis, traverses the paper cylinder 

 in two points. The distance of the second point from the 

 diameter passing through the first, serves to measure the arc 

 described by the system during the passage of the projectile 

 in the interior of the hollow cylinder. 



It is incontestable, after this description, that the funda- 

 mental idea of the process, by which a circular is compared 

 with a rectilinear motion, belongs to Mathey ; but without 

 entering into any detail on the inconveniences of this ma- 

 chine, which no doubt have been the cause of its being 

 little used, we shall content ourselves with obser%'ing that 

 the apparatus of colonel Grobert differs from it essentially. 



1st, By the horizontal position of its axis of rotation. 

 The result of this difference is, that the axis can never be 

 met by the projectile ; which makes it easy to ascertain the 

 solidity and regularity of the position and motion of the 

 disks. 



2d, The projectile does not traverse a cylindric surface, but 



twa 



