The Etruscans, who flourished fifteen hundred years before Christ, and who were much given to the study of nature, are said to have observed the tendency of lightning to make for points, but no theory upon the subject has come down to us from them. Electricity for the ancients was an unplumbed ocean, whose slightest fluctuations affected them in ways they could not understand. In vain they appealed to their gods to help them to explain the enigma. Olympus turned a deaf ear to their prayers. Their imagination exhausted itself in researches into the nature of such things as amber, in which they recognized the curious attribute of attraction and repulsion for objects of slight weight. The poets attributed it to the tears of Phaëton's sisters, lamenting over the dreams of Eridan. Certain naturalists regarded it as a kind of gum issuing from trees during the dry days. No one gave any thought to electricity, by whose subtle fluid the earth and everything upon it is penetrated and enveloped. The superstitions connected with lightning would furnish forth material in themselves for a very curious volume of stories--half comic, half tragic. With the Romans the fall of a thunderbolt was always taken as an omen. In the reign of Domitian, thunder was to be heard once so constantly during a period of eight months that the tyrant, frightened by the bombardment from on high, at last cried out in his terror: "Let the blow come, then, where it will!" The stroke fell upon the capitol, and upon the temple of the Flavian family, as well as upon the emperor's palace and the very room in which he slept. The inscription beneath the triumphal statue was even torn away by the tempest and thrown into a neighbouring garden. Otto de Guérike, burgomaster of Magdeburg and inventor of the air-pump, was the first person to discover the means of producing the electric spark, about 1650. About the same time, Dr. Wall, while watching electricity being released from a roll of amber, noticed a spark and a sudden sharp report, suggestive of a minute flash of lightning, followed by a minute peal of thunder. The analogy was striking. This discovery opened out a new horizon to physicists, and almost immediately the feeble electric light produced by the hand of man came to be associated with the monstrous sheaves of fire let loose in space by unknown forces.