“The lanterns were so constructed as to clasp round the masts and traverse upon them. This was effected by constructing them with a tube of copper in the centre, capable of receiving the mast, through which it passed. The lanterns were first completely formed, and fitted with brass flanges; they were then cut longitudinally asunder, which conveniently admitted of their being screwed together on the masts after the vessel was fully equipped and moored at her station. Letters a a show part of one of the masts, b one of the tackle-hooks for raising and lowering the lanterns, c c the brass flanges with their screw-bolts, by which the body or case of the lantern was ultimately put together. There were holes in the bottom and also at the top connected with the ventilation: the collar-pieces e and g form guards against the effects of the weather. The letter h shows the front of the lantern, which was glazed with plate-glass; i is one of the glass shutters by which the lamps were trimmed, the lower half being raised slides into a groove made for its reception; k shows the range of ten agitable burners or lamps out of which the oil cannot be spilt by the rolling motion of the ship. Each lamp had a silvered copper reflector l placed behind the flame.”
Fig. 11.
The reputation of my father’s catoptric apparatus was not, it appears, confined to those interested in the welfare of the seaman. In 1819, Mr. Stevenson was waited on by a gentleman passing hurriedly through Edinburgh, who came on behalf of Mr. Harris, the manager of Covent Garden Theatre, who was desirous to try catoptric apparatus for certain stage effects which he intended to introduce in London. The proposal seems rather to have taken the Lighthouse Engineer by surprise, but on learning that the gentleman who had favoured him with a call was Mr. Benson, the famous singer of the day, he wrote the following letter to Mr. Harris:—
“I had some conversation with Mr. Benson of your theatre on the day he proposed to leave this for London. The purpose of his visit to me was to inquire about the reflectors we used in the lighthouses upon this coast, which are under my direction, as he had some plan in view for dispensing with the footlights on the stage by the introduction of reflected light.
“Being desirous to give every facility to Mr. Benson’s views, I offered him the loan of a reflector, which I showed him; but from his being on the eve of setting off, and wishing to keep the discovery, if practicable, for your theatre, I agreed to send it to you at Covent Garden, and this letter is to acquaint you that a case containing the reflector and its burner was shipped to your address.
“You are to understand that there is no charge whatever to be made; I only request that the reflector may be returned when you have made your trials. I no sooner learned that I conversed with the gentleman who sings so delightfully in ‘Rob Roy’ than I felt an irresistible inclination to oblige him.
“Wishing you every success in the projected improvement in lighting the stage, I remain,” etc.
The reflector was duly returned by Mr. Harris. The note intimating its shipment says—“It is an excellent reflector, but it collects the light too much in one spot for our use; I mean, it does not spread the light sufficiently about.”
I mention this small matter, not so much because the manager of Covent Garden Theatre came to Edinburgh to get his information, but to show that Mr. Harris’s experiment, made in 1819, foretold the result of all trials that have since been made to light railway stations, public gardens, and parks, by using lighthouse apparatus, which is designed to condense the rays of light, and not to diffuse them, and is therefore inapplicable for such purposes.
* * * * *
The remarks I have made on lighthouse illumination refer to what is known as the catoptric system, whereby the light is acted on by reflection alone. The invention of the dioptric, system by Fresnel was first communicated to Mr. Stevenson in a letter received from Colonel Colby of the Royal Engineers, who had an opportunity of knowing the benefit of Fresnel’s dioptric light in making certain trigonometrical observations for connecting the Government surveys of the shores of England and France across the English Channel. The letter is in the following terms:—
“Tower, 1st Nov. 1821.