8'25 Means of measuring the initial Velocity 



give it sufficient length ; and by lowering the cannon it is 

 thus possible to traverse the disks in different directions in- 

 clined to the horizon. It may be remarked that the pro- 

 jection of the surface of the disks on the plane perpendi- 

 cular to the line of firing decreases more and n)ore in pro- 

 portion as that line inclines ; but this is a very small in- 

 convenience, as the greatest decrease which takes place in 

 the ratio of about 7 to 3, leaves still a suHicient field for 

 pointing^ with all the precision requisite. 



It will not, perhaps, be so easy as might at first be be- 

 lieved to adjust the wheels, the pulleys, and the engage- 

 ment, in such a manner as that the two disks may turn ex- 

 actly together ; we are, however, of opinion that there is 

 nothing in this part of the apparatus which may not be 

 made by any careful ingenious workman. Besides, if the 

 machine be strong, and the parts well executed, there are 

 means of avoiding the errors resulting from the want of co- 

 'incidence which might exist in the motion of the disks. 

 These means consist in counting the turns of the wheels 

 made from the n)oment w hen the piece is fired till that 

 when the machine Stops, and causing these wheels to make 

 the same number of turns in a contrary direction, and in 

 such a manner that the wheels shall be brought to the 

 same respective positions in which they were when the 

 piece was fired. 



We shall suppress several details relating both to the in- 

 clined range and to different pieces of mechanism invented 

 by colonel Grobert for supplying the attention and hand of 

 man in the experiments. By means of these pieces of me- 

 chanism the moving power, when it arrives at that point of 

 its course where its motion becomes uniform, rests on two 

 triggers, one of which causes a pendulum that swings se- 

 conds to oscillate in order to count the time, while the 

 other establishes a communication between the motion of 

 the windlass and that of a system of toothed wheels and 

 pinions, furnished with an index to count the revolutions 

 of the wheels. The weight, when it arrives at the lower 

 extremity of its course, presses on other triggers which 

 serve to set fire to the cannon, and to stop the counter of 

 time and that of the number of turns. These different 

 means maybe useful, but it is sometimes attended with 

 inconvenience to add too many parts to a piece of mecha- 

 nism, and to make it so con)plex that it becomes liable to 

 he deranged. 



As the above explanation will be suflicicnt to give an idea 

 of the niility that may be derived from the apparatus of co- 

 lonel 



