But the very mystery that has always surrounded it has given it an enduring interest, and from time to time there have been certain philosophers whose experiments and discoveries in this subject alone would have been sufficient to place their names high on the roll of scientific fame.

Dr. Gilbert, an English physician, published a book in the year 1600, in which he gave all the facts that were then known about magnetism and electricity, and laid down some general laws in regard to them. Previous to this, amber, jet, and a few other substances were supposed to be the only bodies that would attract other bodies to them when rubbed, but Gilbert's investigations showed that this property was common to many other things, and gave a list of such substances as possessed it.

A half century later than this, the first electrical machine was made by Otto von Guericke, a German philosopher. This machine consisted of a sphere of sulphur—one of the substances which Gilbert described as having the power of attracting light bodies when rubbed; the sphere was made to rotate around an axle, and with this simple apparatus Guericke's experiments were carried on.

In using this machine Guericke first noticed the electric spark, which was so feeble, however, owing to the small power of the sulphur, that it could only be seen in the dark; also, by placing his ear quite close to the sulphur, he was able to hear the sound which always accompanies the spark. Guericke also noticed that the sulphur ball, when rubbed, would at first attract light substances and afterward repel them, although he did not know the reason of this.

Later on Hawkesbee found that amber or glass rubbed with flannel would produce light, and that the same result would follow if two lumps of sugar were rubbed together; and that many other substances had the same property.

Afterward it was discovered that all electrical substances, i.e., bodies which attract light substances when rubbed, will also become luminous by friction. This was the first important general law discovered by experiments in electricity.

In the eighteenth century the English scientist, Stephen Gray, found that electricity would pass from one body to another, though the same experiments proved that this was not always the case, and that in fact certain bodies, called conductors, would receive electricity from other bodies, while other substances, called non-conductors, would not receive it. Gray also established the conducting power of fluids, and of the human body.

These were discoveries of vast importance, and showed, as nothing else could have done, the great advance in science from the days of the old Greeks, who thought that the only electrical bodies they knew owed their power to a breath, which could no more be transferred to another substance than the lily could give its perfume to the rose. Many of the practical uses of electricity, among them the electric telegraph, are based upon this discovery of Gray.

Du Fay, a French scientist who was induced to study the subject by becoming interested in Gray's writings, also made one of the greatest discoveries in electricity. Guericke's observation that electrical substances would at first attract and then repel light substances, was made a subject of experiment by Du Fay, who was finally led to the astonishing discovery that there were two kinds of electricity: one kind—such as is developed by rubbing glass with silk—which he called vitreous electricity, and the other—such as is developed by rubbing sealing-wax with flannel—which he called resinous electricity, and that the two kinds always attract each other; while, on the contrary, a body charged with vitreous electricity would repel another body charged also with that kind, and the same would be true of bodies charged with resinous electricity.

One of the most important discoveries in the history of the science followed soon after, namely, that the two kinds of electricity existed in all electrical bodies, and that the rubbing simply separated them, and that one kind was never produced without the other.

To this period also belongs the discovery of the Leyden jar, an electrical instrument in which large quantities of electricity may be stored up and kept; a metal coating on the inside of the jar being charged with one kind of electricity, which is kept from escaping by the attraction of the opposite electricity on the outer coating of the jar, the two being separated by the non-conducting jar itself. When the two coatings are connected by a conductor the electricities rush together and the jar is discharged. While experimenting with this instrument a Dutch scientist experienced the electric shock, a sensation which caused him considerable alarm, for although it had been known from the time of the ancients that the torpedo could transmit a powerful shock to the human body, it was supposed that the power belonged to that animal alone, and the discovery that this sensation could be produced by an electrical machine made a great impression on the public mind. The Dutch experimenter declared he would not undergo the experience again for the crown of France; but after the first fear had passed away and subsequent experiments had given the operator greater control over the machine, it became quite the fashion for the people to take an electric shock, just for the novelty of the thing, and the Leyden jar became as popular a plaything as the first telescopes and microscopes had been.

Still another great discovery in electricity was made in the eighteenth century, by Benjamin Franklin, whose work for science is none the less interesting from the fact that he was distinguished in many other ways.

Franklin was born in Boston, in 1706, and was the tenth son of an English mechanic who had settled in America, and followed the business of a soap-boiler and tallow-chandler. The father was a man of worth and of strong religious principles, and from the old fashion of giving a tenth of everything to the church as tithes, intended to devote Benjamin to the ministry.

But poverty compelled him to give up this idea, and at ten years of age Benjamin was taken from school and made to assist his father in boiling soap and making candles. This business seemed tiresome to the boy, who was of an ambitious turn of mind, and besides had his head filled with romantic ideas about the glory and charm of a life at sea, and would have liked nothing better than to run away and become a pirate or buccaneer, had chance offered; but for all that, he did well the small duties that were assigned him, it being a part of his character always to do thoroughly what he set about; and after two years at soap-boiling he left his father's shop, and became an apprentice to an older brother who was a printer in the same town.

Here his work was more congenial, for he had an opportunity of reading more books than he had ever had access to before, and reading had always been one of his greatest pleasures; and being fond of books, the making of books seemed to him much more interesting than another trade. He set himself to learning the printer's calling with a good will, and very soon became a very creditable apprentice. His young fellow-workmen took a kindly interest in the boy who was among the youngest of their number, and seeing his fondness for reading, lent him all the books they owned; and as Benjamin also in time made acquaintance with the various booksellers with whom his brother had dealings, he was able sometimes to borrow books from them, often sitting up all night to read a book which had to be returned in the morning. But yet his taste for reading did not entirely destroy his inclination toward a life of adventure, and his predilection for pirates was as great as ever, though by this time he had given up the idea of running away to sea in a ship which floated a black flag; and when it became noised about that Blackbeard, one of the most notorious pirates of the day, had been captured, Franklin's imagination was immediately excited by the event, and he at once set about the composition of a poem of which Blackbeard was the hero, and in which he gave his fancy great freedom, and mixed up bold metaphors and bad rhymes to an appalling degree. This production, together with another one celebrating a shipwreck which had just occurred, was printed and sold about the streets of Boston by the young author, who was immensely flattered at seeing his verses so eagerly seized by the public, and conceived the idea of leaving the printing office and turning poet. But on being assured by his father that poets were generally beggars, and being confirmed in this belief by his reading, he gave up the idea of distinguishing himself in poetry, and turned his attention to prose. And as was his fashion, he set himself to the matter with all the seriousness of his nature, taking for his model the works of the best English writers, and studying them with the greatest care, first reading the articles, then thinking them over till he had the subject well in his mind, and finally writing down his impressions and comparing them with the original. And although this work at the time seemed to his family but the pastime of a restless boy, yet it bore fruit long afterward, when the force and purity of Franklin's style, both in speaking and writing, were of incalculable value not only to himself but to his country.