ELECTRIC LIGHTING

AND

ITS PRACTICAL APPLICATION.

CHAPTER I.

HISTORICAL AND DESCRIPTIVE.

THE application of electricity to the production of light is of but recent date, even as a scientific discovery; and as a matter of practical use for commercial purposes, it goes back but a very few years.

Sir Humphrey Davy, at the Royal Institution in 1810,* by breaking the continuity of the circuit of an electric current emanating from a battery of 2000 cells, and by separating slightly the two extremities of the broken circuit, produced a most brilliant light in an archlike form in the intervening space. The name of the "voltaic arc" has been given to this strip of light; while that of " electrodes" has been assigned to the two points between which the arc is formed. The temperature of this luminous space was found to be so high, as to necessitate the points at either extremity of it being of the most refractory substance to prevent their being fused by the

*Lecture at the Royal Institution on "The Electric Light," by Prof. Tyndall, Jan. 17th, 1879.

B

heat. Various substances have been tried, but two carbon rods, first used by Sir Humphrey Davy, have been found to answer the best: platinum, kaolin, and other substances have also been employed. In the voltaic arc produced between two carbon points, a large portion of the light, it is generally supposed, is due to the passage of incandescent particles of carbon across the space between the points.

It can be readily understood that, brilliant as was the result of Sir Humphrey Davy's experiment, to produce electric light by the chemical means adopted, it was too costly for aught save experimental purposes. Its more general production lay dormant therefore pending the discovery of a more economical producer. It was not till 1831, that the great and important discovery of Faraday of induced currents first foreshadowed it. In July 1820 Ersted, a Dane, by showing that a magnetized needle was affected by the proximity of an electric current, proved the analogy which existed between electricity and magnetism. Ampère and Arago followed it up, and demonstrated more clearly the interaction between the two kinds of currents. But it remained for Faraday, following in their wake, to show that a magnet could create an electric current; or more exactly, that the approach or retrogression of a magnet to or from a bar of soft iron with thin copper wire coiled round it, or, as it is generally termed, an electro-magnet, would induce an electric current in the latter.

The simple apparatus, causing the revolution of such a coil before the poles of a permanent magnet, constituted in fact the first magneto-electric machine-the mechanical motor required to give practical effect to Sir Humphrey Davy's discovery; and which dispensed with the use of any battery or chemical agency. Many years, together with

the work of many minds, were still to be spent before this scientific discovery of Faraday's was to be moulded into such a shape, as to fulfil the requirements of practical and regular application.

Pixii, in Paris, in 1833 constructed a machine in which, by means of a hand-winch, the poles of a horse-shoe magnet were made to revolve rapidly in front of the ends of a double induction coil. Saxton, and afterwards Clarke, inverted this arrangement, and caused the coil, the lighter of the two, to revolve instead of the magnet.

In apparatus of this nature it will readily be seen that the nature of the current induced in the coil, whichever be the revolving element, will be subjected to a series of reversals in direction consequent upon the proximity alternately of the positive and of the negative pole of the magnet. The resultant current is therefore what is termed an "alternating" one.

If it is desired to convert this current into one having a regular, uniform direction, or what is called a "continuous" one, recourse must be had to a device termed a commutator; which takes off each kind of electric current separately.

The presence, or not, of this commutator with a machine at once divides all electric-light machines, whatever be the nature of their construction, into two classes; those of the "continuous," or of the "alternating" direction current.

L'Abbé Nollet, professor of natural philosophy at the Military School at Brussels, perceiving that a powerful electric current might be obtained by a combination of a number of Clarke's machines acting together, devised, about 1849, such an apparatus; its ultimate object being the decomposition of water. Unfortunately he did not survive to see the full success attained by his machine.

The machine, as constructed, consisted of six circular sets, each of four compound horse-shoe magnets, fixed symmetrically; they were arranged on a wooden and iron frame, each set being placed vertically with a space separating it from the next one. In this intervening space rotated a light brass wheel with twenty induction coils arranged round its periphery, which were acted upon by the horse-shoe magnets on either side of it, and in close proximity to which it revolved. From each of these coils the two wires were taken to platinum electrodes, placed in as many bottles as there were coils. All the rotating discs were placed upon a single axle, which was driven by steam power.

Six of these machines were made, and in 1853 taken to Paris under the auspices of the Société Générale de l'Electricité. A public trial of them, to disengage gas for illuminating purposes by the decomposition of water, took place there in the latter part of that year in the courtyard of the Hôtel des Invalides. The illuminating-gas bubble proved a ridiculous failure; and the question then arose as to what to do with the machines.

Mr. F. H. Holmes, who was present at the trial, suggested that they should be utilized in the production of the electric light; and he was empowered to make the necessary alterations for the purpose. A fortnight later at the same place he was enabled, with the aid of one of Duboscq's old form of lamps, to produce a strong and steady light. He made use of a continuous - direction current, having devised a complicated commutator for the purpose, and drove the electric machine at the rate of 700 revolutions per minute. M. Joseph van Malderen, originally employed under Nollet, and who subsequently as foreman engineer (contremaître ingénieur) of the Com

pagnie de l'Alliance put up the electric-light machines in the French lighthouses, assisted in making the alterations requisite. On this memorable occasion many scientific and other well-known persons, both English and French, were present; amongst whom were Lord Howard de Walden, Wheatstone, Brewster, Becquerel, Leroux, Devigne, Duboscq, &c.

In 1854 Holmes designed a machine expressly for the production of the electric light; it was constructed in the Rue Fontaine St. Georges, at Paris. In April 1857 took place the trials of the Holmes machine at Blackwall, under the direction of the Trinity House. Faraday was present, and was so pleased at this the outcome of his own discovery, that he exclaimed to Holmes: "It is my baby, you know, but you have made a man of my infant." This growth to man's estate had taken over a quarter of a century!

The result of these trials, extending over three months, proved so satisfactory to the Brethren of the Trinity House that on December 8, 1858, the South Foreland lighthouse, near Dover, was first lit up by the electric light by one of Holmes' machines; which later on was transferred to Dungeness.

Meanwhile, in France the Compagnie de l'Alliance was being formed about 1859 to take up the construction of electric-light machines, based upon the arrangement of Nollet. After satisfactory trials in Paris, the southern of the two lighthouses at Cape La Hève, near Havre, was lit up by electricity on December 26, 1863, and the northern one on September 1, 1865; since which dates respectively electricity has been regularly used as the illuminant in both. The lighthouse at Cape Grisnez, near Calais, followed on February 15, 1869.

The important part in electrical machines, which is