years of the eighteenth and the earlier years of the present century. The discoveries of Galvani and Volta revolutionized the science of electricity. The pile or battery of the latter was a powerful instrument for research, which, in the hands of hundreds of experimentalists, was rapidly working out the brilliant beginnings of an age of discovery destined to rival all others in the development of the physical sciences. Through the labors of Rumford, Davy, and others, the idea of the unity of the forces of nature begun to prevail. A belief in the close relationship of electricity and magnetism existed generally among scientific men, and the age was ripe for the splendid discovery, made in the winter of 1819-20, through which that relationship was revealed.

Its author was Jean-Christian Oersted, a Dane. The son of an apothecary who practised his profession in a village of less than a thousand inhabitants, his early education was intrusted to a wig-maker and his wife, who taught him to read his mother-tongue and also German. So quick in learning and so attentive was the child, that the amateur schoolmaster ventured to offer him a little instruction in arithmetic, his own knowledge of the subject being confined to addition and subtraction. He was soon beyond the possibility of receiving aid from his

master, but the kindness of others in lending him books rendered such assistance unnecessary. At the age of twelve years he entered the pharmacy of his father as an apprentice. It appears that this was a momentary disappointment to him, as he had resolved, even at that early age, to devote himself to the study of theology. The operations of the laboratory, however, soon excited in him an interest in chemical experiments, which led to an enthusiastic perusal and study of all chemical works within his reach, and undoubtedly contributed greatly to lay the foundation of his future career. He exhibited a taste for all learning, however, studying Latin and Greek, and at this early period showed a fondness for poetry and rhetorical studies, which he retained until the end of his life. Indeed, the degree of doctor of philosophy, which he obtained in Copenhagen at the age of twenty-two years, was granted upon the presentation of a thesis in metaphysics. A year later he was enabled to travel on the continent of Europe, visiting the principal cities of scientific activity, and charming all who came in contact with him by his modesty, as well as by the evident brilliancy of his genius. His career was definitely fixed in the direction of experimental science, and during his years abroad he saw much of the rapid develop

ment of the science of electricity, which had just received so powerful an impetus through the discoveries of Galvani and Volta. On his return he was appointed professor of physics in the University of Copenhagen. He was a skilful and enthusiastic lecturer, attracting large audiences on account of the eloquent and spirited manner in which he presented difficult subjects, his treatment of them being also clear and logical. During the succeeding period of fifteen years, he produced numerous original papers of great value, and he was greatly occupied in the consideration of electrical phe

nomena.

Through his philosophical studies Oersted had become fixed in the belief in the unity of the forces of nature, and he had, in common with others, expressed the opinion that magnetism would one day be found to be related to electricity. He had often tried to discover the connecting link, but hitherto all attempts had ended in failure. It was in the winter of 181920 that his efforts were crowned with success, and his victory was won in the presence of many besides himself. It was during the inspiration of a lecture before his pupils that the thought occurred to him to try a new mode of attack. A battery of considerable power was on the table, and near by was a suspended mag

netic needle. He announced to his hearers what he was about to try, and then seized the wire joining the two poles, and placed it parallel and over the needle, but without touching the latter. Instantly the needle swung out of its position, and one of the most magnificent discoveries of modern science stood revealed as an accomplished fact. Oersted thoroughly worked up the experimental part of his discovery, and published it to the world about the middle of the year 1820.

If there was something dramatic in the way in which this discovery was made, there was something not less so in the manner in which it was seized upon by one of Oersted's contemporaries, developed, extended, and made to serve as the foundation for a tolerably complete superstructure, the science of electrodynamics.

The creator of this science was André Marie Ampère, born at Lyons, France, in 1775. Living at a time when France was rich in men of genius who were devoted to the physical sciences, no other contributed so much that is lasting in the literature of electricity as he, and the annals of the science nowhere exhibit a more brilliant performance than his analysis and extension of Oersted's experiment. On the 11th of September, 1820, he first learned of the

Copenhagen experiment, in which a magnetic needle was deflected by the electric current. On the 18th of the same month, in a paper presented to the academy, he announced the fundamental principles of the science of "electrodynamics." In the almost incredibly short time of one week he had worked over Oersted's discovery both theoretically and experimentally; he had made the capital discovery that magnetic effects could be produced from the current without the use of a magnet; he had shown that parallel wires, through which currents were flowing in the same direction, ought to attract each other, and he had proved by experiment that they did. To do this, he devised novel forms of apparatus, which are to be found to-day in every physical cabinet; and, finally, he had devised an ingenious hypothesis which brought the whole subject within the domain of mathematical treatment. It is safe to say that the science has at no other time advanced with such tremendous strides as during that memorable week.

On this joint work of Oersted and Ampère the whole structure of modern electricity may be said to rest, and with the establishment of this, its almost ample foundation, their names will ever be inseparably connected. Almost sufficient it was, but not quite, for the work of