Pendulum Bob Research Articles

A Measure of Progress in the Mechanical Operations of Arithmetic

record to be kept of the progress of different pupils in the mechanical operations of arithmetic. A simple means is here suggested. The device is valuable for other purposes also, since it stimulates pupils to learn number combinations and helps to bring them up to a definite standard of efficiency. All that is needed in the way of materials is a cord about four feet in length, a weight sufficiently heavy to serve as pendulum bob, and a support that will allow the pendulum to swing clear of the wall. Interest in the use of the device is easily aroused. The teacher suspends the pendulum, having its initial length such that it will vibrate slowly. By way of concrete example, let us consider its use in a fourth grade where the multiplication tables are still troublesome, and the simple number combinations are still unmastered. The pendulum is set in motion, at first at its maximum length, therefore at its maximum time periods. If the drill desired is in addition, let the teacher announce a constant, as six. After the class has the constant well in mind, some starting-point is announced, as nine. In concert the class gives the results of successive additions of six, starting with the base nine: Nine, fifteen, twenty-one, twenty-seven, etc. It will be surprising how many drop out as the numbers grow larger. Here is a sifting process. If this were the only value, it might be worth while; but the greatest value of the device lies in the accurate measure of attainment at any period of arithmetical work. The pupils who drop out early in the concert recitation are urged to suspend such pendulums at their homes and drill themselves, shortening the pendulum as fast as possible. The length of the pendulum is recorded and furnishes a measure both accurate and universal in application. 348

Pendulum Seismometers

PENDULUM SEISMOMETERS are among the oldest forms of instruments employed to record earthquake motion upon a stationary plate. In 1841 crude forms of such seismometers were used to record shocks at Comrie in Scotland. The objections to the older forms of these instruments are that they are not provided with any arrangement to magnify the motion of the earth, the writing indices are not sufficiently frictionless, and the value of the records are destroyed because the pendulums almost invariably swing (see “Experiments in Observational Seismology,” by J. Milne, Trans. Seis. Soc., vol. iii. p. 12). The first pendulum seismometer with which I am acquainted which has a multiplying index is the one described, constructed, and successfully employed by Dr. G. Wagener (see Trans. Seis. Soc., vol. i. p. 55). From Dr. Wagener's account of this instrument it was the inventor's intention to counteract any tendency of the pendulum bob to swing by the inertia of the multiplying index, and from his experience with the instrument, owing to frictional resistance or otherwise, it seems that even if the pendulum was set in motion it quickly came to rest.