West Australian (Perth, WA : 1879 - 1954), Tuesday 17 March 1896, page 6


ROTTNEST LIGHTHOUSE.

DESCRIPTION OF THE STRUCTURE.

His Excellency the Governor will perform the ceremony of turning on the light in the new lighthouse at Rottnest to-day. A number of leading gentlemen have been invited by the Premier, Sir John Forrest, to be present at the ceremony, which will take place at noon.

The following description of the structure will, no doubt, be of interest.

The new lighthouse is situated on the highest point on Rottnest, close to the site of the old building, which dates back for fully 50 years. From the base to the top of the lantern the new tower is Cart. high, with a diameter of 14ft. The lantern placed in the summit is of octagonal form, lift, in height, and is surrounded by a gallery. The lightkeepers'qnarterB are Bicnatedinthebass of the tower. The structure presents a plain appearance, forming a mo stive, rooms

mented column of stone. The foundations are built of concrete, and are 152ft. above high-water mark. The tower itself stands 12ft. high, with the appliances, etc., for serving lampe. Around the lantern, as already stated, is a gallery enclos- d with a substantial iron railing. The focal plane of the lantern is 264ft. above high-water mark. At 400ft from the ground 1 level the cap of the structure forms a gallery 3ft wide running round the lantern. A massive doorway gives entrance to the lowest chamber, in which are stored the tanks containing

supply of oil. Iron spiral staircases lead from floor to floor through the four other chambers to the lantern. The stairs have been imported from England and are of special design. The successive floors of the various storeys are of checked plates on rolled steel joists, and in the fifth storey or service room is placed the light.

The following description of the light is supplied by the Public Works Department The light is a first order Holophotsl lievolving Light of 920 millimetres focal distance, constructed by Messrs. Chance Bros. & Co., Ltd., Birmingham, to the order of the Government. The pedestal and revolving carriage are of the usual Change pattern The pedestal is squire and contains the actuating clock with the accompanying gearing Hand relating gear is also supplied. The block weighs 5cwt., the rate of descent bring about 10ft. per second. The clock will me for a period of approximately three hours without re-winding. The revolving carriage is fitted with hardened steel roller paths on which conical steel rollers are traversed. The rp the is borne on the upper roller path. In addition gun metal horizontal rollers are fitted to maintain the optic in a central position. The optical apparatus consists of eight panels, each subtending a horizontal -angle of 45 degrees. The vertical angle of the fences in 57 degrees, of the upper part ma 48 degrees, and of the lower prisms 21 degrees. The nppir.prisms in each paid number 18, the central leaves eight, and the lower prisms eight. to one panel the lower prisms are omitted for convenience in entering the apparatus. The whole is carried with strong gun-metal framework, suitably stayed. The pressure lamp is of the " Chance " pattern, having a capacity of 12gals., with suitable gearing. The four burners (three to span) area of the usual Trinity House old pattern. These are arranged for consuming heavy mineral oil of about 25deg. Fahrenheit flashing point (close tent), with a specific gravity of '828. The ventilating tube is of the usual dimensions, and provided with efficient damper genriDg and spare parts.

On testing the rotation of the optical op. parades with the burner in action, the period of the flushes and eclipses was found to be as follows: Flash Base., eclipse 17sec; flash 3300., eclipse 17sec. ; fUsh Face., eclipse 17sec; flush See., eclipse 17sec. ; flask 3 sec, eclipse 17sec. ; flash 3sec, 17sec. ; flush 3sec. 17sec. ; period,

20sec. One revolution 2min. 40sec. The

dip of the beam of light emanating from the apparatus is 420 millimetres. The candle power of the six-week burners gives an average Service result per burner of 730 standard candles with six weeks in action. The consumption of heavy mineral oil with six weeks in action in 803 fluid ounces per hour. It is the practice to have the six weeks in action only during fogs and impaired atmo-spheres. During a clear atmosphere the 'inner works are turned down and suppressed by means of deflectors, which latter are supplied for the purpose.

The calculated efficiency of the beam emitted from the optical apparatus is 730 standard candles, with an intensity of beam

of 45-162 standard candles.

The design was produced in the Works Department, under the direct supervision of the Assistant Engineer-in-Chief, from data supplied by Mr. W. T. Douglas, the wellknown lighthouse expert and adviser to the Trinity House brethren. The contract for the erection of the tower was undertaken by Messrs. Parker and Rhodes, and the foundation stone was laid by the Premier, Sir John Forrest, on the 25th of April last year. The time limited for the completion of the contract was the 31st of May this year, and it will therefore be seen that the contractors have finished their work in advance of the time.