[ 220 j 



XXXIV. Report on ilie Meam of measjiring the hutial 

 Vuoiily of Projectiles thrown from Cannon, loth in an 

 inclined and a horizontal Direction. Read in the Phy- 

 sical and Mathematical Class of the French National 

 Inslitute iti the Monih of December 1804*. 



JL HK class charged Messrs. Bossiit, Monge, antl inyself, 

 to give in a report on the means for measuring the initial 

 velocity of projectiles thrown from cannon, proposed by 

 colonel Grobert, who constructed an apparatus of such di- 

 mensions that we could employ it for our preliminary cx- 

 periuicnts. This apparatus was as follows : 



A horizontal revolving axis, of about 34 decimetres in 

 letigth, has at each of its extremities a disk or circle of 

 pasteboard placed perpendicular to the axis, the centres of 

 which are in the same axis, to which it is fastened in such 

 a manner that the whole svstem can turn rapidly without 

 the respective positions of its dilTercnt parts being deranged. 



The rotary motion is communicated to the axis and to 

 the disks by means of a weight suspended at the extremity 

 of a rope, which, after passing over a pulley raised ten or 

 twe've yards above the ground, rolls itself round the arbor 

 of a wheel and axle fixed at the same level as the disks. An 

 endless chain, which passes round on the one side the wheel 

 of the axle, and on the other a pullev fixed on the axis of the 

 doks, transmit to that axis the motion which the weight 

 communicates to the wheel and axle during its fall. 



This. apparatus, as is seen, has the merit of being simple^ 

 and without entering into further details it may be readily 

 conceived how it can be employed for measuring hori- 

 zontal velocities. Let us suppose that the two disks are 

 £» rest, and that a ball traverses them in a direction pa-r 

 ra'i'el to the axis or the line passing through their centres ; 

 it ':? mai.ifest that this axis will be in the same plane with 

 the holes m^de in the disks; but if the disks turn around 

 their axis while the ball passes from the one to the other, 

 th^ plane containing the axis of rotation and the first hole 

 v'il not coincide with the second hole; and if a second 

 plane be made to pass through the second hole and the axis, 

 the angle formed by these two planes will he the measure 

 of the arc described by any point of the disks, while the ball 

 or bullet passes ever the interval by which they are sepa- 

 rated. 



* From the Journal des Mines, Florcai, an 12, no. 92. 



