CAUSES OF DRIFT. 245 
THE CHAIRMAN—It only remains for me to thank the lecturer very 
much for his interesting lecture, which has led to such a very interest- 
ing discussion. JI am afraid we are not unanimous as to drift yet. 
Ye ae dee SONI D)ILDC IL 
INSTRUMENT FOR SHOWING THE MOTION OF AN ELONGATED SHOT 
DURING FLIGHT. 
The diagram on the next page represents the plan of an instrument 
made for me, by Mr. Colbrook, modeller of the R.M. Academy, Woolwich, 
to show the motion of an elongated shot when projected with or without 
rotation at a low velocity. The shot A, is made of box-wood, and is about 
d inches long and 2 inches in diameter ; it is supported in two metal 
centres in the axis of a movable frame, B B B, which can slide up or 
down in the grooves, shown by the dotted lines, in the side pieces 0 0. 
The side pieces are attached toa table, HH, which can be raised and 
fixed at any required angle of elevation to another lower table by means 
of the screw m. 
To project the shot, the frame is drawn down until the metal eye a 
can be placed over the pin b, two gutta percha springs, D D, being very 
much stretched to allow of this. As may be seen in the diagram, one 
end of each spring is attached to the hind cross piece of the frame, and 
the other end to a pin, J, fitting into a hole in the side piece. cdisa 
metal spring, and when the end ¢ is raised, the eye is suddenly lifted 
off the pin, the frame is released and moves rapidly up the side pieces 
until checked by the wooden pins ee, which have a gutta percha wad 
over each to lesson the strain upon them. The front cross piece of the 
frame, g h, is not attached to the rest of it, but flies off when the motion 
of the frame is checked, the shot being therefore free to move forwards. 
The velocity being low, the exact position of the axis may be easily 
observed. The range may be varied, as with a gun, by elevating the 
table, or by changing the position of the pins 7/ so ag to increase or 
decrease the tension of the springs when the frame is drawn down. 
The greatest range at 45° is about 30 to 35 feet. 
