The following is a simple and useful contrivance for the prevention of accidents in raising men or minerals out of mines, by the ropes " running wild," as it is termed, and for which the inventor, Mr. E. Speers, was presented with the silver Vulcan medal by the Society of Arts. A bar is fixed on the end of an axis. Two hooks, as A, swing freely on the ends of this bar ; C is a short bar or stop, projecting from the frame of the machine, for the hook to catch hold of. When the bar re volves at a moderate rate, the hooks constantly hang down by their own weight, and keep clear of the stop C; but when it revolves with a dangerous rapidity, the centrifugal force causes the hooks to diverge from their pendant position, and one of them catches hold of the check-bar C, (as shown by dotted lines,) which stops the machine instantly.
A correspondent in the Register of Arts proposes the following modification of this contrivance, by which the shock occasioned by the sudden stoppage of the machinery is avoided, and the further advantage gained, that when the velocity of the machinery is so far reduced as to avoid danger, the machinery will not stop, but will recommence motion of itself. In the engraving in the next page, a is a section of Mr. Speers' check-hooks ; the bar to which the hooks are sus pended turns with the axle b e; e is a conical pulley, with grooves cut it a spiral direction, as represented in the section ; this pulley turns on the axle, and not with it, like the bar a i out of this pulley projects the check-pin f.
G is a screw fixed to the frame h, which fits into the pulley e, so as to enter it as soon as the pulley is made to revolve in the same direction as the bar a. i is a cord fixed to the pulley e, so as to be wound round all the grooves when the pulley is turned ; to the end of it is fixed a weight, the size of which must be regulated according to the velocity with which the machine is required to work. From inspection of the plan it will be seen that when the check-hooks, by the too rapid revolution of the check bar a, have diverged so far from their pendant position as to lay hold of the check-pin f, the pulley e will be drawn round in the same direction as the bar a, and will wind the weight suspended by the cord i until the cord reaches the uppermost groove, as at 1, when the velocity of the machinery will be greatly moderated, at which time the pulley e will have advanced so far along the screw G as to draw the check-pin out of the check-hooks, when the machinery will proceed in a regular way, and the cord i, by the descent of the weight attached to it, will reverse the motion of the pulley, and return it to its original position, as shown at i, where it will be always ready to regulate the machinery when the check-hooks, by their centrifugal force, come in contact with the check-pin f.