HAVING in our last number described the buildings and floating vessels from which beacon lights are exhibited, we have now to give some account of the nature and history of the lights themselves.

At a very remote period, when the early mariners of the world first ventured to extend their sea-voyages beyond the few hours of daylight, or of moonlit nights, the want must have been felt of warning and guiding lights, and the more especially as those primitive voyagers, who were the first pioneers of commerce, must have perpetually " hugged " the shore, their chief fear being, that they should be carried away by an " off-shore" wind into the great unknown region of waters extending they knew not whither.

In the first part of this paper, we have referred to the ancient state of the buildings specially constructed for the exhibition of beacon lights, and of which there is historic record; but far, very far beyond that age must we carry our mental vision in imagining the period when the first signal-fires were piled on the hill-side, or rocky point, or overhanging cliff, to guide the absent mariner safely to his home again.

Interesting, however, as it may be, as a subject for reflection and conjecture, to trace the gradual development of human progress in all matters, from the rude and simple state of a remote and ignorant barbarism to the comparatively complex and refined civilization of the present time, we have now rather to do with the practically useful than with the sentimental; we shall therefore proceed at once to describe the successive improvements in the great sea-lights of a later age.

There can be no doubt that all the earlier lights were simply fires of wood. The Tour de Cordaan, when completed in 1610, I was provided with an iron chauffer or cage in which faggots of wood were burned; and in our' own country, where coal is more abundant than in most others, open coal fires were sometimes adopted, a light of which description was actually in use at the Isle of May, on the coast of Scotland, from the time of the erection of its light tower, in 1636, until so late as the year 1816, when a new tower was built, and was provided with oil lamps and reflectors.

No less than 400 tons of coal were latterly burnt each year in maintaining this light. i The disadvantages of this primitive mode of illumination were manifold. The degree of intensity, size, and even cok ur of the light must have been very variable, the distance at which it could be seen being equally so; it did not admit of any distinctive marks by which one light could be distinguished from another; the quantity of fire consumed was enormous, and its supply must, in proportion, have involved great labour and expense; while the waste of light was likewise great, since it shone in all directions, towards the land as well as towards the sea, and upwards to the sky. It is, however, recorded of the wood and coal fires as an advantage, that, in wet and foggy weather, their reflection was distinguishable high up in the air when they were not themselves visible.

The next change appears to have been first adopted at the Eddystone, at which, from its isolated position, being several miles from the land, it would have been very difficult to maintain a sufficient supply of fuel in the winter months. Its illuminator was accordingly composed of twenty-four wax candles, surrounded by a glass lantern, but without reflectors, or any other artificial means of increasing or concentrating the light; and insignificant as it must have been, compared with the splendid lights of the present day, the plan was yet a considerable step in advance of the open fires.

The next great improvement in sea-coast lights was the adoption of reflectors, which, like many other improvements in the various departments of art, science, and manufactures, appears to have been the immediate result of accident rather than of deliberate design and forethought.

Before, however, proceeding to describe the successive advances in the science of pharology, or the branch of " Optical Engineering," as it has been termed, which' applies to sea-coast illumination, it will be desirable, for the information of unscientific readers, that, without going deeply into optical details, we should briefly explain the principles on which science is made available to produce such truly valuable practical results.

Kays of light travel through space in all directions, and in straight lines, unless diverted therefrom by reflection from the surface of an opaque body, such as silvered glass or polished metal, or by refraction in passing through transparent bodies, as glass or water. If then two diverging rays of light, or bundles of rays, can be thrown, either by reflection or refraction, on one point, thus occupying the space of one ray or bundle of rays, the intensity or brightness of the light on that point will be doubled: if twenty rays are thus made to converge into the space of one ray, the brilliancy at the point of convergence or focus will be increased twentyfold. A familiar instance of this principle, by refraction, exists in the common glass lens, vulgarly called a " burning glass," which, by throwing a large number of rays of light on one point, produces an intense light and heat, capable of exploding gunpowder and igniting inflammable bodies. In the same manner, the shape of a mirror or reflector may be so arranged as to collect the rays of light emitted on one side of a luminous body, and to throw them forward, so that they shall converge in a point, or series of points, on the opposite side, and thus being added to the direct rays, increase the intensity of the light on that side.

A concave mirror, the curve of which is a parabola, is found to be the necessary form to effect the object in view, and a series of such reflectors, attached to lamps suitably adjusted, thus collect the useless rays of light from above, below, and behind, and throw them forward in a horizontal direction.

As stated above, this system, which has been denominated the catoptric or reflector system, from the Greek word KO.- roTrrpov, a ' mirror,' was the first that was employed in the improvement of beacon lights. It is essentially the English system, both from its having been originated and been longer retained here than in other countries.

The credit of first introducing it has been claimed both by England and France. Undoubtedly, however, the earliest application of reflectors was made in England, whilst to France belongs the honour of very greatly improving them.

Somewhere between the year 17&3 and 1767, Mr. WILLIAM HUTCHINSON, the dockmaster at Liverpool, first applied a parabolic reflector to his flat-wicked lamps. The idea is stated to have thus originated. A convivial company of-scientific men met at Liverpool, when one of the company present wagered that he would read a book by the light of a farthing candle, at a [distance of 200 feet from it. The wager was won by means of a wooden bowl, lined with putty, in which facets of looking-glass were embedded, forming a reflector. Hutchinscn was present, and seizing the idea, utilized it for his lighthouses. His reflectors were formed of tin plates, or of wood lined with looking-glass, the largest 13 feet in diameter with 6 feet focus, being placed behind a " spreading burner mouthpiece" 14 inches broad. The Ridstone, Hoy: lake, and Leasowe lighthouses were thus illuminated, and they were undoubtedly excellent lights for the period.

Fig. 1.

Mr. Hutchinson's reflector, &c.

In the year 1786, the Northern Lights Board fitted reflectors and lamps of a similar description, at the Isle of May and Cambrae Isle lighthouses in the Firths of Forth anc Clyde. These were said to have been the invention of Mr. Thomas Smith, the engineer to the Board; but whether or not he was aware of similar reflectors having been adopted elsewhere, is not known.

On the other hand, in France, a M.

Tealere, a member of the Royal Corps of Engineers of Bridges and Roads in that country, is said to have first proposed the use of parabolic reflectors; and the celebrated Corduan light-tower was illuminated in that manner about the year 1780, by M. Lenoir, under the direction of the Chevalier Borda.

The reflectors were made of sheet copper, plated with silver, and the lamp then just invented by M. Argand, of Geneva, since known as the Argand lamp, was adopted.

These great improvements then became general in other countries, and at once advanced the system of lighthouse illumination into a science. The reflectors of the present day are made precisely in the same manner as M. Lenoir's, of copper thickly plated with silver, very highly polished, and, like his, lit by Argand burners, having a cylindrical flame of about one inch in diameter. The form of those now in vise is that calculated by Captain Huddart, an Elder Brother of the Trinity House, in 1791. They are very durable, many of the reflectors still used remaining unimpaired after 30 and 40 years' continued service.

The size adopted by the Trinity House is 21 inches diameter for lighthouses, their sectional area being 346'3 square inches, and 12 inches diameter for light vessels, with an area of 113 square inches. Some reflectors are said to multiply the brilliancy of a light as much as 450 times. Catoptric lights are capable of nine distinct variations, viz., fixed revolving white, revolving red and white, revolving red with two whites, revolving white with two reds, flashing, intermittent, double fixed, and double revolving. The first exhibits a steady and uniform appearance.

The reflectors used for it are of smaller dimensions than those employed in revolving lights, and which is necessary in order to allow of their being ranged round a circular iron frame, with their axes inclined at such angles as to enable them to illuminate every part of the horizon (Fig. 2). The revolving light is produced by the revolution of a frame with three or four sides, having reflectors of a large size grouped on each side, with their axes parallel; and as the revolution exhibits a light gradually increasing to full strength, and in the same gradual manner decreasing to total darkness, its appearance is extremely well marked (Fig. 3). Eighteen, twenty, and even thirty reflectors are thus arranged on the faces of the revolving framework.

The succession of red and white lights is caused by the revolution of a frame whose different sides present red and white lights, and these, as already mentioned, afford three separate distinctions, viz., alternate red and white, the succession of two white after one red, and the succession of two red after one white. The flashing light is produced in the same manner as the revolving light; but by a different construction of the frame and greater quickness of the revolution, a totally different and very striking appearance is produced.

The brightest and darkest periods being but momentary, the light is characterized by a rapid succession of bright flashes, whence it derives its name. The intermittent light is distinguished by bursting suddenly into view, and continuing steady for a short time, after which it is suddenly eclipsed for many seconds, ordinarily in English lights for about half a minute. Its peculiar and striking appearance is effected by the perpendicular motion of circular shades in front of the reflectors, by which the light is alternately concealed and displayed. The double lights, which are commonly only used where there is a necessity of a leading line, for taking some channel, or avoiding some danger, are exhibited from two towers, one of w hich is higher than the other, and the two lights when seen in one vertical line, form a direction for the course of shipping.

The following diagrams and explanations will, we hope, make the general character and arrangement of the lamps and reflectors Fig. 2.

of the catoptric lights sufficiently intelligible to the general reader.

Fig. 2 shows a plan, in section, of one tier of reflectors arranged in the manner employed in a fixed catoptric light: n n shows the chandelier, q the fixed shaft in the centre, which supports the whole, o o the reflectors, and p p the fountains of their lamps.

Fig. 3.

Fig. 4.

Fig. 3 represents a plan, in section, and Fig. 4 an elevation of a revolving apparatus on the catoptric principle. In these figures, » n shows the reflector frame or chandelier, o o the reflectors with their oil fountains, p p. The whole is attached to the revolving axis or shaft, q.

Fig. 5 is a sectional view of a single parabolic reflector and lamp, representing one of the series shown in Figs. 2, 3, and 4. Its action is due to the peculiar properties of the parabolic reflector, which throws forward or reflects all rays of light that impinge on it from its focus, F, in lines parallel with its axis; so that if the lamp and reflectors be placed in a vertical position, the whole of the rays will be thrown forward horizontally. Such reflected rays are represented by the lines F af, F b b', Fee', Fd d', and F e e'. If the light were a mathematical point, it is obvious that the united rays of light collected and thrown forward by the reflector, would form merely a cylindrical beam of light, or bundle of rays, of the diameter of the reflector itself, and that the collected light would thus be only visible from within the.

limits of its own narrow circumference, the light appearing, when viewed from all other positions, of its natural size and brilliancy alone, as if no reflector were employed.

As, however, the light itself, from the circular wick of an Argand lamp of one inch in diameter, is of considerable size, and parts of it are therefore removed from the true focus of the reflector, there is a considerable divergence of the reflected rays, which is of the utmost value, and alone gives to the reflector its character of practical utility.

Thus by ranging a series of such lamps and reflectors round a circular frame, the divergent rays so spread out, combine and cross each other, and form a complete band or belt of light, which may thus be made to cover the whole horizon, and embrace all objects moving on the face of the waters or the land within its scope. This angle of divergence, in one of the reflectors ordinarily in use, represented in this figure by the angle m Vn, is equal to 14° 22', and it would require twenty-four such reflectors to form a complete circle of light. In the figure, the point V represents what is called the vertex of the reflector—the line V Z its conjugate axis. A is the fountain of the lamp, and S the shaft or portion of the frame on which it is fixed.

We have, so far, endeavoured to make plain to the general reader the origin, growth, and character of one of the two systems by which the sea-coasts of the civilized world are now illuminated. It is the elder of two beautiful sisters, whose pure and beneficent charms will probably yet, for a long time, continue to be reflected on the ocean's waves, and to attract the seaman's wistful gaze.

We will not risk the chance of any disparaging or otherwise invidious comparisons between two objects, each having such great claims on our admiration and gratitude : we therefore postpone our humble tribute to the latter until our next number, and now conclude with the reflection that few objects are more calculated to impress on our minds the beneficence of the Great Author of all things, who has thus caused man's general welfare, worldly prosperity, happiness, and progress so greatly to depend on the use of those mental faculties with which He has gifted him, and the industrious exercise of which, whilst it conveys a blessing on his race, should, at the same time, be ever looked upon by him as his greatest happiness and roost glorious privilege.