Not that scientific investigations in that or any line were pushed very assiduously in those days, for there is a great gap between the discovery of the property above alluded to and the acquisition of any more solid knowledge pertaining to electricity. The phenomenon was at that time set down in the list of natural facts, and no attempt appears to have been made to connect it with others. The inquiring spirit of the present age can hardly be brought into more striking relief than by a comparison of the, at present, almost daily advances in scientific knowledge with the fact that twenty-two hundred years elapsed between the discovery of the above-mentioned power of amber by the ancients and the later one that a very large number of other substances, such as diamonds, vitrefactions of all kinds, sulphur, common resin, etc., possess the same property. A few other scattered facts were, however, also noted by the ancients: fire is said to have streamed from the head of Servius Tullius at the age of seven, and Virgil asserts that flame was emitted by the hair of Ascanius. In examining, now, the history of the rise of electrical science we find, as just mentioned, the vast gap of over two millenniums between the discovery of the attracting power of rubbed amber and the mere extension of man's knowledge so as to include other substances. The philosophers Boyle and Otto von Guericke, who were active during the latter half of the seventeenth century, added a mass of new data in this line. Boyle, moreover, discovered the equivalence of action and reaction between the attracting and the attracted body, and that the rubbed amber or other "electric" retained its attractive powers for a certain period after excitation had ceased.