A great invention is never completed by one man. It was to be expected that the electric light would be improved. A number of kinds of incandescent light have been devised, using different kinds of filaments and adapted to a variety of uses. The original Edison carbon lamp, however, continues in use, being better adapted to certain purposes than the newer forms.
The mercury vapor light deserves mention as a special form of arc light. In the ordinary arc light the arc is formed of carbon vapor, and the light is given out from the tips of the white-hot carbons. In the mercury vapor light the light is given out from the mercury vapor which forms the arc. This arc may be of any desired length, and yields a soft, bluish-white light which is a near approach to daylight.
The Telegraph
The need of some means of giving signals at a distance was early felt in the art of war. Flag signals such as are now used by the armies and navies of the world were introduced in the middle of the seventeenth century by the Duke of York, admiral of the English fleet, who afterward became James II. of England. Other methods of communicating at a distance were devised from time to time, but the distance was only that at which a signal could be seen or a sound heard. No means of communicating over very long distances was possible until the magnetic action of an electric current was discovered. When Oersted's discovery was made known men began to think of signalling to a distance by means of the action of an electric current on a magnetic needle. A current may be sent over a very long wire, and it will deflect a magnetic needle at the other end. The movements of the needle may be controlled by opening and closing the circuit, and a system of signals or an alphabet may be arranged. A number of needle telegraphs were invented, but they were too slow in action. Two other great inventions were needed to prepare the way for the telegraph. One was the electromagnet in the form developed by Professor Henry, a horseshoe magnet with many turns of silk-covered wire around the soft-iron core, so that a very feeble current will produce a magnet strong enough to move an armature of soft iron. The magnet has this strength because the current flows so many times around the iron core. Another need was that of a battery that could be depended on to give a constant current for a considerable length of time. This need was met by the Daniell cell.
The electromagnet made the telegraph possible. The locomotive made it a necessity. Without the telegraph it would be impossible to control a railway system from a central office. A train after leaving the central station would be like a ship at sea before the invention of the wireless telegraph. Nothing could be known of its movements until it returned. The need of a telegraph was keenly felt in America when the new republic was extended to the Pacific Coast. An English statesman said, after the United States acquired California, that this marked the end of the great American Republic, for a people spread over such a vast area and separated by such natural barriers could not hold together. He did not know that the iron wire of the telegraph would bind the new nation firmly together.
The Morse telegraph system now in use throughout the civilized world was made possible by the work of Sturgeon and Henry. Sturgeon's electromagnet might have been used for telegraphy through very short distances, but Henry's magnet, with its coils of many turns of insulated wire, was needed for long-distance signalling. In one of the rooms of the Albany Academy, Professor Henry caused an electromagnet to sound a bell when the current was transmitted through more than a mile of wire. This might be called the first electromagnetic telegraph. But the application to actual practice was made by Morse, and the man who first makes the practical application of a principle is the true inventor.
In 1832, on board the packet-ship Sully, Samuel F. B. Morse, an American artist, forty-one years of age, was returning from Europe. In conversation a Doctor Jackson referred to the electrical experiments of Ampère, which he had witnessed while in Europe, and, in reply to a question, said that electricity passes instantaneously over any known length of wire. The thought of transmitting words by means of the electric current at once took possession of the artist's mind. After many days and sleepless nights he showed to friends on board the drawings and notes he had made of a recording telegraph.
In New York, in a room provided by his brothers, he gave himself up to the working-out of his idea, sleeping little and eating the simplest food. Receiving an appointment as professor in the University of the City of New York, he moved to one of the buildings of that university and continued his experiments in extreme poverty, and at times facing starvation, as his salary depended on the tuition fees of his pupils.
A story told by one of his pupils describes his condition at the time.
"I engaged to become one of Morse's pupils. He had three others. I soon found that the professor had little patronage. I paid my fifty dollars; that settled one quarter's tuition. I remember, when the second was due, my remittance from home did not come as expected, and one day the professor came in and said, courteously: