THE CAPE SCHANK LIGHTHOUSE.

Press, Volume VII, Issue 797, 19 May 1865, Page 3

THE CAPE SCHANK LIGHTHOUSE.

A correspondent of the Australasian gives a description of a visit to the lighthouse at Cape Schank, from which we extract the following: — ___ie lanthorn of tho establishment is elevated at about 50 feet above the ground, upon a stone tower of most substantial character. Arriving at the door of this, and pro - ceeding to ascend the winding steps of solid stone let into the massive walls, one seems to experience a sensation of proceeding up stairs into a cellar; soon after there comes a strong odour of heated oil, as from an engine room ; next is heard an uninterrupted clackclacking, as though a dozen turret clocks were severally and togetherrunning down in a very agony of desperation ; going further, the odour grows still stronger, and the turret clocks still more demonstrative ; at last we catch a faint gleam of light, and immediately find ourselves in that particular part of the building where all mystery seems likely to be explained. To examine the whole effectually we climb yet a little higher, up a light* iron ladder leading into the very lanthorn itself This is a circular room, a dozen or so feet in diameter, surrounded by a continuous window. Outside there runs a narrow balcony, guarded by a brass rail, and used both as a look-out and a means of cleaning the glass. In this room there is yet another lanthorn of a peculiar form. A very little attention shows that the latter is slowly revolving, so

that every side—it has six or eight—is, in rotation, turned towards a particular point. In one of the sides there is a doorway, admitting of a passage into the interior. There being ample room, and to spare, for even a larger party than our own, we, on invitation to do so, stepped within. In the centre there blazes one of tbe very largest of argand lamps, and that of a description so peculiar that it must be alluded to more particularly. Of course a good light is a desideratum in all establishments of this description. For fifty years the farfamed Eddystoue itself had no better illumination than that afforded by twenty-four tallow candles; but this light of other days has brightened and not faded. Gas, of course, is out of the question ; electric light, at a future day, may supersede all others for such purposes;" but at present, the grand resource of lighthouse management is in oil, Any one acquainted with chemistry knows that, to obtain a good light from any material, the combustion must be perfect. If this is not the case, then instead of a bright white flame we shall get a dull and smoky one, simply that the whole of the materials are not completely burned, and that the carbon is given off as black smoke, which settles on any cold object as soot. This does not so much arise from the nature of the combustible, as on whether the flame is properly supplied with oxygen. Turpentine or camphine, when the latter requirement is attended to, burns with an exceedingly bright light-giving flame, but otherwise more carbon is deposited from lamps fed with such substances than, perhaps, from any other. When a flame fed by oil is small there is no great difficulty in keeping it a bright one. but soon as ever the wick is enlarged beyond a certain point smoke is given off, and the illuminating power is rather diminished than increased ; simply that there must be portions of the flame which no oxygen can reach. To remedy this is the object of the argand burner. In this a circular wick produces a hollow flame, and as.air thus passes up through the very centre of the burning gasses, and, moreover, in a current of some considerable force, plenty of oxygen is supplied, and the combustion is, to all intents, perfect. Even this kind of burner has its limits. A wick of small thickness can only supply oil enough for a small combustion ; and if the wick is made indefinitely thicker, then as in a common single-wick lamp, part ofthe burning gases will be unsupplied with oxygen, and so give off carbon, as before. The remedy for this in lighthouse lamps is to use a number of wicks, arranged one within the other, so that the whole form a number of concentric circles, a space being left between each pair, through which the air has a free passage

But these wicks must be supplied with oil ; and here, so fierce is the flame and rapid the consumption, that the mere capillary attraction of the wicks, depended up on in common lamps, is found to be insufficient for the purpose. A very ingenious employment of the surplus power used to keep the lanthorn in motion is made to work three or four miniature pumps, and by these a continuous supply of oil is forced, as it were, through the wicks, and that in such ample quantities, that a stream runs over at the top and falls into the reservoir below. Even the power of this stream is not wasted, but is employed that a very trustworthy telltale is provided, to warn the keeper should the requisite supply of oil happen to fall short. To do this the surplus oil is made to fall into a small brass cup, with a hole in its bottom, and fixed to the end of a lever. As the hole spoken of cannot carry off so large a volume of oil as the stream supplies, the cup is kept full, and acts by gravity in keeping the end of the lever depressed. No sooner, however, does the steam diminish than the cup is speedily emptied; the end of the lever, released from its weight, flies up, detaches a catch, and starts an alarum, warning the man on duty that the oil needs replenishing, and besides securing him, as I hope, a lecture from the head keeper for neglect of duty.

Even this perfection of light and contrivance for the supply of oil is by no means all that has to be done to render a lighthouse efficient. Shakespere tells us how far a little candle throws its beams, but neither a little candle nor a large one—no, nor a large burner such as that described—would be seen far out at sea on a hazy night, and this particular lighthouse is fully expected to be sighted at over thirty miles distant. We know how a common lamp throws its rays in all directions—up, down, and towards every point of the compass indiscriminately. If we place a looking glass behind such lamp, so as to arrest a portion of the rays, the space behind the glass will be unilluminated, and that in front will receive more light than ordinary. This is one of the simplest methods of obviating a waste of light and throwing the same in the direction where most required. If instead of a plane looking glass we use a concave mirror or reflector, another object will be gained—the light thrown forward will be in parallel not in diverging rsays, so that whether at a few yards or at many miles distant, the reflected light will fall upon an object with nearly the same intensity. This is not a consequence of the light being really increased, but that it is deprived of its usual divergent properties, and instead of radiating so as equally to illuminate all the space around, it is thrown forward in, as it were, a compact cylinder of luminous rays, and just in the direction where light i* most Nearly the same object is achieved by placing a large lens before instead of a mirror behind the light. Whilst the former is called the catopric, the latter it known as the dioptric, j principle—a carriage lamp with its reflectors j illustrates the one, a policeman's bull's-eye is no inapt representation of the other. It is on the latter principle that the Cape Schank lighthouse has been constructed. Of course, when there are these contrivances for concentrating a great amount of light on certain spots, there must jemain a large circle which does not obtain any illuminating power whatever. Hence the neces-

sity that the lenses should revolve, so that the concentrated rays may, in turn, fall upon every part of the horizon. Hence, too, it is that, looking at a lighthouse, it seems to flash, blazing up one minute and almost going out the next. When we are in a line which passes through the plane of the lens at right angles, of course we get the maximum of its illuminating power; in every other situation we see the light diminished, or we look upon almost total darkness. But the mystery of the phenomenon as shown us by Mr 3. Jones is not yet solved. If you rememmber, the alternation was —a dim light, a tolerably bright gleam lasting some 40 or 50 seconds followed by a second period of dimness, then a dazzling flash, the I duration of which seemed scarcely a single ! second, and then dimness once more. This arrangement, however, is peculiar to the lighthouse under consideration, and is enjoj'ed in common wit h no others on the coast Were it otherwise, all trust and confidence in lighthouse guidance would be at an end; for if a ship coming in from a long voyage after dull weather made a light, and there were no signs to show whether the same shone on Cape Schank, Cape Otway, or at Port Philip Heads, most disastrous consequences must result. By day, therefore, such buildings are distinguishable from each other by different colors. Different colored lights at night might answer a similar purpose, but for various reasons it is found better to adopt another method, and classify them on the charts and sailing directions by the duration of their steady light, flash, and obscuration. Let us see how this, too, is managed. The inner lanthorn has, we will say, eight sides. Four of these are ground into the form of a plano-convex lens (like a common bull's-eye), which throw light towards the horizon in a compact cylinder of parallel rays. -Four are ground in such a way that horizontally their sides are parallel, but vertically they also appear to nave a lenslike form, these throw the light towards the horizon, it is true, but while the rays vertically are parallel, horizontally they spread over a considerable space. When either of the four sides so shaped are turned towards the spectator he sees a moderately well-defined light, lasting a considerable time. As the lanthorn revolves, the part where two sides meet at an angle is turned in the same direction ; this is the period of obscuration. In time, the spectator's live of sight cuts the lens-like side at right angles (which is tne only line in which light passing through this side can be seen at all), and then there is the dazzling flash. Lastly, another angle presents itself, and another obscuration follows, after which the same order is repeated. So it is that these guardians of our coast tacitly, yet effectually, make their nightly signals. Far away on the sea the mariner sees them, sights to cheer and beacons to guide. The Government of England and the Governments of all English dependencies display a most commendable zeal to have their lighthouse services well attended to. Few persons there are who must not see the necessity of the institution in this, so essentially a commercial colony ; and so I trust the time may not be considered as thrown away which I spent in visiting this lion at Cape Schank, or in writing of what I saw there.