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.

This course of study, together with the advantage he received from the conversations that were carried on in his brother's shop, in which all the important questions of the day were discussed, led in time to another attempt at authorship, but this time Franklin acted in secret from fear of ridicule, and slipped his manuscript under the office door, where it was found the next morning by his brother, who read it aloud to his friends all unconscious that the author stood by trembling with suspense, lest his judgment should be unfavorable.

But the paper was well received, and printed in the newspaper which was published at the office, and from this time Franklin made several contributions to the same paper before the name of the author was found out.

At this time Franklin was about sixteen years of age, and considering that he had not been at school since he was ten, and that all his chance for study had to be taken out of his few leisure hours, he was a tolerably well-informed lad. He was of a very practical turn of mind, and listened to all the discussions on political topics with a keen interest and many a suggestive thought of the remedies that might be applied to existing evils. But his brother, who misunderstood the boy's nature, was not calculated to develop his young charge, and as he had always exercised over him a petty tyranny that was most aggravating to the younger brother, the time came at last when Franklin decided that it would be better for them to part.

He said nothing of his plans to anyone, knowing full well that he would only meet with opposition, but selling some of his books to obtain money, he took passage on a sloop that sailed between Boston and New York, whither he had determined to go. He left home in the night, secretly, and so really ran away at last, though only to become a harmless printer instead of the daring buccaneer he had once imagined himself.

But on reaching New York, which at that time contained only one printing-office, Franklin failed to obtain work, and so pushed on to Philadelphia, where after many ups and downs he finally succeeded in getting the promise of a printing-office of his own, and recommendations to people in England, where it was necessary for him to go to buy the needful outfit.

But Franklin found that the friend he had depended upon had failed him at the last moment, and he reached London without any letters of recommendation and with very little money, and found it necessary to work at his trade in order to get the means to return.

This experience, however, was not lost upon one who turned all the events in life to some use, and when after eighteen months in England Franklin returned to Philadelphia, he found himself possessed of the newest processes in printing, besides having picked up much other useful information.

Soon after his return to America Franklin started a debating society among his young friends, which was called the Hunto, or Leather Apron Club, because every member was supposed to be a mechanic, and in this society the young printer soon occupied a leading position.

Here were discussed all the political questions of the day, and also various philosophical subjects, and the interest that was then awakened in such discussions led to the most important results; for much of the ease and straight-forwardness which distinguished Franklin as a political speaker later on, could be traced to the exciting and inspiring debates in the Junto Club, while many of the practical plans for the benefit of the public which were suggested by Franklin, owed their origin to the same source.

The first circulating library in America was started by the Junto Club, and began with fifty subscribers, and all of Franklin's plans for improving the condition of the city were laid before his fellow-workmen in the Junto before being made public.

These plans were so practical and of such undoubted value, that before long Franklin's name was associated with every movement connected with the public life of the city, and the citizens of Philadelphia came to have such a high regard for the man who had so often proved their benefactor, that it was sufficient for them to know that Franklin approved of any plan to give it their heartiest support.

In this way it came about that the public service was raised to such a degree that Philadelphia became a model city among the colonies.

The circulating library was followed by the establishment of a night patrol for the protection of the city, and which was supported by taxes on property; then came the organization of the first fire brigade, which met with such success that in a short time most of the prominent citizens became members of it, every member pledging himself to furnish a certain number of the bags, buckets, and baskets which constituted the working utensils of the company. Then came the founding of the American Philosophical Society in 1743, the headquarters of which were fixed in Philadelphia; and a few years later the Junto Club started a movement which immediately became popular through the exertions of Franklin, and which resulted in the founding of the University of Pennsylvania.

The first hospital built in Philadelphia was largely due to Franklin's influence, people refusing to subscribe to it until they heard that he considered it desirable. Franklin also first called attention to the streets of Philadelphia, which were at that time unpaved and generally in a filthy condition. He first succeeded in having a walk paved in one of the principal streets, and as it soon became splashed with mud form the road, suggested that the houseowners should each pay a small sum to have the pavement kept clean. But paving the streets, when once it was started, seemed do desirable a thing to the inhabitants, that in a very short time the whole city was rendered lean and comfortable by paved streets. Then some one suggested that the streets should also be lighted, and lamps were brought from London for that purpose, Franklin again showing his practical turn of mind by substituting square chimneys of four panes of glass for the original globes which became speedily dimmed by the smoke; and this care for details and interest in the small concerns of life was also shown by the invention of the Franklin stove, which was a great advance over the wide, open, draughty chimneys which had hitherto been used for all household purposes, and by some wise suggestions about a cure for smoky chimneys.

In fact, Franklin never considered that any matter which concerned the welfare and comfort of his fellow-men was unimportant, and would set himself just as readily toward abating some perplexing household annoyance, as to solving a question in philosophy, claiming always that the aim of all knowledge should be the practical serving of the human race.

In the troubles between the colonies and the mother-country which preceded the Revolution, Franklin showed the full powers of his mind, and was a tower of strength to the people. Never weary of planning, advising, and working, he was an example of firmness of purpose united to unceasing labor, and his courage and perseverance at this critical time were of inestimable value. He was among the first to claim and insist upon the rights of the colonies, and declared that justice must be maintained if every law of man should be broken in the attempt. But, notwithstanding his bold stand at this time, Franklin's wise and temperate judgement did not allow him to be carried away by any of the enthusiasms which were at that time popular among the more excitable class of colonists. He did not advocate separation from the mother-country if justice could be obtained without that step, and claimed that he was a loyal American only because he was a loyal Englishman. But when the crisis came, and England proposed to do as she pleased with her own, regardless of all principles of right and justice, and when the English Parliament voted money for forcing the colonies to submission at the point of the sword, then Franklin, who had been in England during the troubles, trying to arrange matters on a peaceful basis, at once declared that the time for entire independence had come, and that the question would never be settled until the American colonies had become a separate nation. And all through the dangerous and disheartening years of the Revolution, he was the firm friend and unwaverng supporter of the struggling colonies. He was one of the signers of the Declaration of Independence, and a few months afterward was appointed Commissioner to the French court, where he remained during the war, and where his influence in behalf of his country proved of incalculable value. And when the struggle was over, and the United States took their place among the nations, the treaty of peace which acknowledged the independence of America, was signed by Franklin, who was the American representative.

Franklin, on his return to America, was made Governor of Pennsylvania, and in less than two years afterward was appointed to take part in drafting the Constitution; and although he was then an old man, he showed the same good judgment and vigor of thought which had always made him such a valuable adviser in public matters.

In his scientific career Franklin was not less illustrious than in his political life. The founding of the American Philosophical Society, which was in constant communication with the Royal Societies of London and Dublin, and of which he was the first secretary, led to a familiarity with the progress of science in Europe, and throughout his long and busy life he never failed to keep up his interest in the scientific pursuits which at that time received such an impetus.

The discoveries of Gray and Du Fay in electricity produced a great impression on him, and his studies in the same department were followed with an absorbing interest. What this mysterious power called electricity was, became the question of the day, and scientific minds set resolutely to work to solve the question.

Franklin's experiments in electricity were confined to the problems of finding out, if possible, what electricity was, and its distribution throughout nature. Gray and Du Fay had shown that there were two kinds of electricity, which repelled and attracted each other mutually, and that the electric current could pass from one body to another. Franklin attempted to find out the reason for this attraction and repulsion, to discover why there existed conductors and non-conductors, or why some bodies would allow the electricity to pass through them and others would not.

After many careful and interesting experiments, he was led to the belief that electricity was not created  or produced, either by friction or any other process whatsoever, but that it was present everywhere, and that every body contained some quantity of this mysterious force, though what its nature was and how great its power might be, no one cold decide. Franklin reasoned that as all bodies were equally supplied with electricity, there would be a state of equilibrium which would show no signs of its existence unless it were in someway disturbed, and that the electricity manifested itself only when something occurred to disturb the normal condition of the body, either by giving it more electricity or taking some away from it.

Instead of the theory of two kinds of electricity, Franklin claimed that all the phenomena connected with the subject could be explained by suppposing a body to contain more or less of electricity, and introduced the words postive  and negative  to illustrate the condition of a body containing more or less than its normal quantity, and suggested that the terms vitreous  and resinous  be supplanted by the words positive  and negative, a body being electrified positively when it received an addition of electricity, and negatively when some is taken from it; and these are the expressions that are now generally used in speaking of the different conditions.

Franklin's greatest contribution to this department of science, however, was the discovery that electricity and lightning are the same thing. The thought that this might be true was not strictly original with Franklin, as Gray and others had hinted it before, but he was the first to make the experiment which proved their identity beyond a doubt.

This discovery, which was destined to make the name of Franklin famous in the history of science, resulted from the simple experiment of drawing the lightning from the clouds by means of a silk kite, to which was attached a pointed wire—Franklin having demonstrated before this the power of points to attract electricity. The experiment was tried in the open field during a heavy thunder-shower, Franklin and his son standing under an open shed which afforded them a shelter from the rain. Franklin at first noticed that the fibres of the kite string which he held in his hand were separating, as in the passage of the electric current, and by means of a small metal key attached to the cord he obtained the electric spark and the shock, and charged a Leyden jar, as well as performing other electrical experiments.

The experiment was thus a complete success and established the identity of electricity and lightning beyond the shadow of a doubt. And although, when Franklin's paper on the subject was read to the Royal Society of London, the learned members greeted it with sneers and laughter, yet the scientists throughout the rest of Europe accepted its views with alacrity, and French, German, and Italian translations were eagerly sought for, and the name of the discoverer of this new secret of nature was spoken of everywhere with admiring praise.

Franklin's practical mind could not rest until he had found some means of applying this great discovery to the benefit of mankind, and the lightning rods which were before long erected on many buildings were among the results which followed his famous experiments; and had it not been for the engrossing political cares which occupied his mind during the long period of his country's need, it is probable that he would have made other inventions which, if not anticipating those at present in use, would at least have proven of much practical benefit in applying the powers of electricity to the concerns of daily life.

Next to the discovery of the law of gravitation, the discovery of the identity of lightning and electricity and its universality throughout nature, was perhaps the greatest truth of nature that had yet been grasped, and Franklin's work for science, though forming only an episode in his brilliant political career, was of such lasting importance as to place his name high on the list of the world's great discoverers.

He died in Philadelphia on April 17, 1790.