An ingenious machine, invented by Mr. Benjamin Robins, for ascertaining the velocity of military projectiles, or the force of fired gunpowder. It consists of a large block of wood, fixed to the end of an iron rod, and suspended like the pendulum of a clock. When the pendulum is at rest, a gun is pointed towards the centre of the block, and a ball fired point blank into it In consequence of the magnitude of the block, compared with the ball s or bullet, a very small velocity is given to the former, which being accurately measured, the velocity of the ball is easily deduced; for, as the weight of the ball is to the sum of the weights of the ball and block, so is the observed velocity of the block to a fourth quantity, which is the velocity of the ball sought. A variety of experiments have been made by Dr. Hutton with this pendulum, from which a number of useful rules have been deduced relative to the velocity produced with different charges of powder, with guns of different lengths, and with different sized balls.

A complete series of experiments was also instituted relative to the resistance of the air to different velocities, varying from 0 to 2,000 feet in a second.

Among other results, he ascertained that inflamed gunpowder expands itself with a velocity of about 5,000 feet in a second.