PARACHUTE. An apparatus resemb ling the common umbrella, but of far greater extent, intended to enable an aeronaut, in case of alarm, to drop from his balloon to the ground without sus taining injury. This is effected by means of the resistance of the atmosphere. When the parachute is detached from the balloon, and abandoned with its load in the air, it must proceed at first, from the continued action of gravity, with an accelerated motion, until the increased velocity produces a resistance equal to the force of attraction, or the weight of the apparatus with its load. After this equilibrium has been attained, the para chute will descend with a nearly uniform velocity. According to theory, this ter minal velocity, supposing the surface of the parachute to be flat, is equal to that which a heavy body would acquire in falling though the altitude of a column of air incumbent on that surface, and hav ing the same weight as the whole appar atus. A circular parachute having a diam eter of 30 feet, and weighing with its load pounds, would acquire a terminal velocity of about 13 feet per second ; and a person descending with it at this rate would receive the same shock on reach ing the ground as if he dropped freely from a height of 21 feet. The actual re sistance of the air is, however, greater than is given by theory, and is, besides, augmented by the concavity of the para chute, which occasions an accumulation of the fluid ; but, on account of the ac tion of the wind, the axis of the para chute will probably become inclined to the vertical, in which case the resistance will suffer a diminution.
One of the most remarkable instances of descent from a great height with a parachute is that of Garnerin, a French man, who ascended in a balloon from London, on the 2nd of September, 1802. After hovering seven or eight minutes in the atmosphere, he cut the cord by which his parachute was attached to the bal loon. It instantly expanded, and for some seconds descended with an acceler ating velocity, till it became tossed ex tremely, and took such wide oscillations that the basket or car was at times thrown almost into a horizontal position. The
intrepid aeronaut narrowly escaped de struction by being precipitated on the houses in St. Pancras, and at last fortun ately came to the ground in a neighbor ing field. He seemed to be much agitated, and-trembled exceedingly at the moment he was released from the car.
A recent experiment of this kind, made by Mr. Cocking, was attended with fatal consequences. Having conceived a no tion that the vibration might be avoided by giving the machine a different form, this projector constructed one in the form of an inverted umbrella, that is, having the concave side uppermost, and bound to a strong wooden hoop to prevent its collapse in the descent. The diameter of the hoop was 84 feet ; and there was also a hole of 6 feet in diameter in the middle of the parachute, which, it was supposed, would also contribute to give greater steadiness. Having attached himself to this machine, he ascended from Vauxhall Gardens on the 24th of July, 1837. On being cut away from the balloon the para chute descended rapidly, and with violent oscillations ; the hoop broke, and the un fortunate projector fell, dreadfully mangled, at Lee, near Blackheath. The persons in the car of the balloon were also placed in great danger, having nar rowly escaped suffocation from the quan tity of gas expelled in consequence of the great velocity with which the balloon darted upwards immediately on being liberated from the parachute. They suf fered extreme pain, and for a time were deprived of sight j but fortunately they had carried up with them a large bag filled with atmospheric air, by means of which they were enabled to breathe. Without this, they would probably have perished. Since then safe descents have been made with the parachute both in England and France.
Latterly, use has been made of these instruments in making descents in coal mines. Occasionally the rope breaks and injury arises. By one of these being attached, when an accident occurs it un furls, and breaking the force of the fall enables those descending to reach the bottom in security.