MANTLET, IRON.

Iron Mantlets for the protection of Markers at Rifle practice are constructed of half-inch plate iron, 7 feet 4 inches high, 6 feet long, and the sides 1 foot 6 inches wide at the top, and 2 feet 6 inches at the bottom. Weight 17 cwt. The mantlet is secured by four screws on each side, which pass through angle, riveted to the mantlet, into wooden baulks underneath.

A Pendulum is readily made (if not in store) with a musket ball, and a piece of silk. The length of a pendulum is measured from the centre of the ball to the end of the loop, on which it swings.

To find the length of a pendulum to make a given number of vibrations.

Rule. As the square of the given number of vibrations is to the square of 60, so is the length of the standard (3914, length for one second) to the length sought.

Or, multiply 39.14 by the square of the time required for the pendulum to vibrate-viz., by the square of, for second; and by the square of 2=4, for two seconds.

To find the number of vibrations, the length of pendulum being

given.

Rule.-Multiply 60 seconds by the square root of 39·14, divided by the length of the given pendulum.

Or say, As the given length is to the standard length, so is the square of 60 (its vibrations per minute) to the square of the number required.

ROCKETS, WAR.

Two kinds-1st. Boxer's improved Congreve. 2nd. Hale's. both there are 3, 6, 12, 24 pounders.

Of

Hale's rocket has no stick, being kept point foremost by the aerotation given from the gas pressing against 3 curved shields fixed to the three vents.

ROCKETS, LIFE SAVING, BOXER 12 POUNder.

These are fixed to carry a line over a stranded vessel, and establish a communication by means of which a hawser carrying a sling, and also a line for running the sling along the hawser are made fast to the highest possible point available on the masts. Two or three men may travel together on the sling. No rule can be given as to speed, which must depend on the distance of the vessel. It is very important to avoid fouling.

MACHINE, ROCKET.

For Congreve rockets there are three kinds-1. Siege. 2. Field. 3. Sea-service. Some modifications will be adopted for Hale's rockets.

To find the number of vibrations, the length of pendulum being

given.

Rule.-Multiply 60 seconds by the square root of 39.14, divided by the length of the given pendulum.

Or say, As the given length is to the standard length, so is the square of 60 (its vibrations per minute) to the square of the number required.

ROCKETS, WAR.

Two kinds-1st. Boxer's improved Congreve. 2nd. Hale's. Of both there are 3, 6, 12, 24 pounders. Hale's rocket has no stick, being kept point foremost by the aerotation given from the gas pressing against 3 curved shields fixed to the three vents.

ROCKETS, LIFE SAVING, BOXER 12 POUNDER.

These are fixed to carry a line over a stranded vessel, and establish a communication by means of which a hawser carrying a sling, and also a line for running the sling along the hawser are made fast to the highest possible point available on the masts. Two or three men may travel together on the sling. No rule can be given as to speed, which must depend on the distance of the vessel. It is very important to avoid fouling.

MACHINE, ROCKET.

For Congreve rockets there are three kinds-1. Siege. 2. Field. 3. Sea-service. Some modifications will be adopted for Hale's rockets.