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His Excellenoy tho Governor will perform the cotomony of turning on the 1-ght in tho new litbthonte at Bottnest to-day. A number of leading gentlemen bave been in- vited by the Premier, Sir John Forrest, to be prêtent at the ceremony, which will take place at noon.

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

The new lighthouse is situated en the highest point on Rottnr-st, close to the Bite of the old building, which dates back for fully 50 years. From the bato lo the top of the lantern the new tower is C2jrt. 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, mioma

mentcd column of stone. The fonndatiens ara boilt of concrete, end are 152ft. nbove high-water mark. The tower itseif stands 122££t. high, with the appliances, etc., for serving lampe. Around the lantern, ^as already stated, is a gallery enclos- d with a pubstantial iron railing. The focal plane of the lantern is 264ft. above high-water mark. At 100ft from the groun 1 level tha osp of the Btrnotnre forms a gallery 3ft wide run- ning reaad the lantern. A massive doorway gives éntranos to the lowest chamber, ia whieh are stored the tanks containing

supply of oil. Iron spiral staircases lead from floor to floor throngh the four other chambers to the luntern. The stairs have been imported from England and are of special design. The successive floors of the various storeys aro of cbesktr plates on rcl'ei iren joists, and in the fifth storey or service room is plaoed the light.

The following desoripHon of the light is supplied by the Publio Works Department : The light is a first order Holophotsl lie volving Light of 920 millimetres foeal dis- tance, constructed by Messrs. Chance Bros. & Co., Ltd., Birmingham, to the order of the Government. The pedestal and revolving carriage are of the usual " Chance " pattern The pidestal íb squire und contains the aetuatiug olock with the accompanying gear- ing. Hand rotating- g°ar íb alao supplied. The olook weighs 5cwt., the rate of de«c9nt biing about 10ft. per second. The clock will mu for a period of approximately three h'-ars without re-winding. The revolving carriage is fitted with hardened steel roller paths on which conical steel rollers a-e traversed. The rp ti o is borne on the upper roller path. In addition gun metal hor'zoutal rollers are fitted to maintain the optio in a central position. Tha optical apparatus con- sists of eight pDnels, each subtending a horizontal -mglo of 45 degrees. The vertical angle of the lenees ia 57 degrees, of the epprr prit ma 48 degress, and cf the lower prisms 21 degrssB. The nppir.prisms in each paml num- ber l8, the central lenses eight, and tha lower prisms eight. Io one panel the lower prisms are omitted for convenience in onterirg the apparatus. Tho whole is oarried with serong gnu-metal framework, saitably stayed. The pressure lamp is of the " Chance " pattern, having a capacity of 12gals., with suitable geering. The four burners (three to span) ara of the usual Trinity Honss old pattern. These are arranged for consuming h?avy mineral oil of abont 235iegs. Fahrenheit flashing point (close tent), with a specific gravity of '828. The ventilating tube is of the UBual dimensions, and provided with effiaient damper genriDg and spare parts.

On testing the rotation of the optical op. paratas with the burner in aotion, the period of the flushes and eclipses was found to bi as follows:-Flash 3aao., eclipse 17e6c; flash 3300., eclipse 17seo. ; fUsh 3aoo., eclipse 17sec; flush Süeo., eclipse 17sec. ; fla«k 3 sec, eclipse 17seo. ; flash 3-ec, 17eeo. ; flush 3sec. 17sec. ; period,

20sec. One revolution 2miu. 40seo. The

dip of the beam of light emanatirg from the apparatus is 420 millimetres. The oandla power of the six-wiek bnrnors gives an average Bcrvice result per burner of 730 standard candios with six wicks in aotion. The consumption of heavy mineral oil with six wicks in action ia 80*3 fluid ounaes per hour. It is the practice to have the six wioks in aotion only during fogs and impaired atmo- spheres. Daring a olear atmosphere the 'inner wioks are turned down and suppressed by means of deflsotors, whioh latter are sup- plied for the parpóse.

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

of 45-162 standard candles.

The design was produced in the "Works Department, under the direot supervision of the Assittant Enginosr-in-Chief, from dita supplied by Mr. W. T. Douglies, the well known lighthouse expert and adviser to the Trinity Honee Brethron. The contract fe- tte erection of the tower was undertaken ley Messrs. Parker and Bhodes, and the founda- tion stone wsB laid by the Premier, Sir John Forrest, on the 25th of April last year. The time limited for the completion of the con traot was the 31st of May this year, and it will therefore bo seen that the contractors have finished their work in advance of the time.