| 摘要 |
<p>A ball (33) is attached to the end of a string (36) mounted in a winding-unwinding device (15) fixed to one of the ends of an adjustable bracket (9) supported by a mast (8) integral with a movable base (1). The ball (33) is kept at a certain distance under the bracket (9) by means of a small ball and a retainer housing (32) adjusted to compensate only for the weight of the ball so that the latter may be released at the smallest shock.</p> |
