some by the ton that, previous to the advent of photography, were only known as curiosities of the laboratory; while the camera-maker has so exercised his ingenuity as to give us cameras of perfect workmanship and almost automatic in their action.

Such have been the birth and progress of photography during the latter two thirds of the nineteenth century. Compared with most other branches of science and art, it is still in its infancy, so that greater improvements may be looked for. But be that as it may, surely enough has been done to make the nineteenth a memorable century to the photographic historian.

PROGRESS OF ELECTRICITY FROM 1800 TO

BEFO

1900

BY JOHN TRowbridge

EFORE the year 1800, the world's knowledge of electricity was confined to observations on the attraction of electrified pith-balls, and to a few facts in regard to electric sparks. Had it not been for lightning, no one could have felt respect for the feeble manifestations of an agency which was destined in less than a hundred years to change the channels of trade, to revolutionise methods of communication, and to light the great cities of the world. Lightning was a portent of all this; but no one yet saw the beneficence in the energy that was so destructive and so terrifying. There was another feeble force, too, of which the world in 1800 knew something-the force of magnetic attraction. This was useful in the magnetic compass; but it was judged to be insignificant in other respects and totally unrelated to the force of electrical attraction, which was manifested in the case of the pith-balls, or to the forces of lightning. No one in the wildest flight of imagination saw it exalted to a Titanic force, capable, by means of its relationship to electrical attraction, of moving all the machinery of a great city.

The marvellous development of electricity which we have all seen seems to carry with it the presumption that we have a clearer knowledge of what electricity is than Benjamin Franklin had; but this presumption is not entirely warranted. We certainly know its relations to

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other forms of motion, such as light and heat, better than he did. We believe that it is a wave motion; but still we cannot fully explain the fundamental experiment of the attraction of two electrified pith-balls. To the philosopher, this confession of ignorance of an agency which he can use intelligently, which is highly serviceable, but the origin of which is completely veiled from us, is most suggestive. The question immediately arises, "To what do we owe our command of this mysterious servant ?" The answer to the question is this: "We owe our advance in knowledge to the careful verification of phenomena, to the improvements in machinery produced by almost microscopic measurements, and to accurate calculation."

The steps which led to our present knowledge of the manifestations of electricity can be quickly told. The first was taken by Galvani, who, just before the last century dawned, demonstrated that electricity could be produced by the contact of metals with fluids. His experiments suggested to Volta in 1800 the electric battery. Here was a means by which an electric current could be produced; and Oersted with this current showed a connection between electricity and magnetism. The current in passing through a wire near a compass-needle could change the reading of the needle, and the changes depended upon the direction in which the current flowed. There seemed to be a suspension and a hush between each of the turning-points in the history of the advance of electricity, which are typified by the stillness before a thunderstorm. Oersted's discovery was made about twenty years after Volta constructed his battery. It was more than ten years after Oersted that Joseph Henry and Michael Faraday discovered another relationship between electricity and magnetism which involved the possibility of producing currents of electricity by the motion of a magnet. This discovery was the converse

of Oersted's; the series of phenomena which it revealed embraced the subject of electromagnetism, and have led directly to the invention of the dynamo and electric motor. The world, however, did not realise in 1831 the importance of the steps taken by Henry and Faraday. Another ten years elapsed before the electric telegraph became a success. Then in 1861,-thirty years from the date of the discovery of electromagnetism,— Paccinnoti invented the armature, which Gramme improved, and we had the dynamo and the electric motor. Again, in a little more than ten years, the telephone came, and the mechanical engineers and the mechanic, thoroughly aroused to the possibilities in the practical employment of electricity, took hold with astonishing energy.

When Tyndall came to America in 1870 to deliver lectures on light and electricity, he brought with him one hundred Grove cells to produce an electric light for the purposes of demonstration. His assistant was obliged to spend two hours before each lecture in arranging these cells, filling them with acids and scraping the connections, retiring from each encounter almost asphyxiated by the irritating and poisonous fumes of nitrous-oxide gas. At the present time no lecturer on science in the halls where Tyndall spoke need spend a moment in providing a source of electricity. It is on tap, so to speak, and can be obtained by touching a button. Tyndall in his highest flight of scientific imagination did not picture development of electricity which would light the halls in which he spoke, which would convey him to and fro with great speed through the streets which he used in going to them, and would enable him to whisper from Boston across the great prairies of the West to St. Louis.

The title of his lectures in Boston was suggestive"Light and Electricity." Yet his imagination, greater than that of most of his contemporaries in science, failed more completely in the subject of light than in the field

of the great practical expansion of electricity. He had no inkling of the coming theory that light is but one of the manifestations of electricity, and in ten years from the date of his lectures would be so regarded by the leaders of scientific thought. When we reflect upon how much this man saw and how much was withheld from him, a feeling of self-abasement comes over us who are students of electricity. Who can foretell what the next hundred years will unveil ?

In reflecting upon the rapid advances in the employ. ment of electricity, we are apt to overlook the aid which has been given by the improvements in the mechanic arts. It can be maintained with a great show of reason that the modern lathe, the milling machine, together with the principle of interchangeable parts in machines, have made the dynamo and the electric motor. It is said that Joseph Henry spent months in wrapping wire with cast-off gowns to insulate it for his experimental electro-magnets. Much more powerful magnets can be wound to-day in half an hour. The mechanical means of trying experiments in the practical employment of electricity have multiplied to such an extent that every mechanic can enter a field which once was occupied by only one man in America, Joseph Henry; and can enter it with the most refined appliances in respect to tools and materials. Many of the men who have aided the practical development of electricity have known little of the subject of electricity. Some who have achieved distinction as electricians were ignorant of even elementary laws; but they saw how machines could be operated by what to them was a fluid analogous in its manifestations of flow and pressure to water. Just as men were ingenious in transmitting power by pulleys, belts, and chains, they now became apt in devising circuits, switches, armatures, keys, and the multitude of devices of which one gets a realising sense in reading the advertisements in the thousand-and-one