Thales and his contemporaries seem to have made no serious attempts to explain the attraction of the rubbed amber, and indeed so little importance was attached to the discovery that it was completely forgotten. About 321 B.C. one Theophrastus found that a certain mineral called “lyncurium” gained attractive powers when rubbed, but again little attention was paid to the matter, and astonishing as it may seem, no further progress worth mention was made until towards the close of the sixteenth century, when Doctor Gilbert of Colchester began to experiment seriously. This man was born about 1543, and took his degree of doctor of medicine at Cambridge in 1569. He was very successful in his medical work, and became President of the College of Physicians, and later on physician to Queen Elizabeth. He had a true instinct for scientific research, and was not content to accept statements on the authority of others, but tested everything for himself. He found that sulphur, resin, sealing-wax, and many other substances behaved like amber when rubbed, but he failed to get any results from certain other substances, such as the metals. He therefore called the former substances “electrics,” and the latter “anelectrics,” or non-electrics. His researches were continued by other investigators, and from him dates the science of electricity. [Illustration: FIG. 1.--Suspended pith ball for showing electric attraction.] Leaving historical matters for the present, we will examine the curious power which is gained by substances as the result of rubbing. Amber is not always obtainable, and so we will use in its place a glass rod and a stick of sealing-wax. If the glass rod is rubbed briskly with a dry silk handkerchief, and then held close to a number of very small bits of paper, the bits are immediately drawn to the rod, and the same thing occurs if the stick of sealing-wax is substituted for the glass. This power of attraction is due to the presence of a small charge of electricity on the rubbed glass and sealing-wax, or in other words, the two substances are said to be electrified. Bits of paper are unsatisfactory for careful experimenting, and instead of them we will use the simple piece of apparatus shown in Fig. 1. This consists of a ball of elder pith, suspended from a glass support by means of a silk thread. If now we repeat our experiments with the electrified glass or sealing-wax we find that the little ball is attracted in the same way as the bits of paper. But if we look carefully we shall notice that attraction is not the only effect, for as soon as the ball touches the electrified body it is driven away or repelled. Now let us suspend, by means of a thread, a glass rod which has been electrified by rubbing it with silk, and bring near it in turn another silk-rubbed glass rod and a stick of sealing-wax rubbed with flannel. The two glass rods are found to repel one another, whereas the sealing-wax attracts the glass.