It was, as I have said, one of the best coal-fires in the kingdom, and three men were employed to keep the bonfire burning, so that its inefficiency as a light was not due to any want of outlay in its support. But its appearance was ever varying, now shooting up in high flames, again enveloped in dense smoke, and never well seen when most required. When Mr. Stevenson visited the island, with a view to its purchase by the Commissioners, he was told by the keeper, that in violent gales the fire only kindled on the leeward side, and that he was in the habit of putting his hand through the windward bars of the chauffer to steady himself while he supplied the fire with coals, so that in the direction in which it was most wanted hardly any light was visible. Nothing can be worse than any variableness or uncertainty in the appearance of a light. Better far not to exhibit it at all than to show it irregularly; and the coal lights were so changeable and destitute of characteristic appearance as to be positively dangerous. This indeed was too sadly proved by the loss of H. M. ships ‘Nymphen’ and ‘Pallas,’ which on the 19th December 1810 were wrecked near Dunbar, the light of a limekiln, on the coast of Haddington, having been mistaken for the coal light of the Isle of May. Fortunately only nine of their combined crews of 600 men perished; but the vessels, valued at not less than £100,000, became total wrecks.
During the long period he held the office as Engineer to the Board, Mr. Stevenson designed and executed eighteen lighthouses in the district of the Northern Lighthouse Commissioners, many of them in situations which called for much forethought and great energy. All his lighthouse works were characterised by sagacity and inventiveness, and exhibit successive stages of improvement, equally indicative of the growing prosperity of the Board and of the alacrity and zeal with which their Engineer laboured in his vocation. Whether we consider the accuracy and beauty of the catoptric apparatus, the arrangements of the buildings, or the discipline observed by the lightkeepers of the Northern Lighthouses, we cannot fail to recognise the impress of that energetic and comprehensive cast of mind which directed the whole. Acting under the direction of an enlightened Board of Commissioners, my father may, with the strictest propriety, be said to have created the lighthouse system of Scotland. His merits indeed in this respect were generally acknowledged in other quarters; and many of the Irish lighthouses, and several lighthouses in our colonies, were fitted up with apparatus prepared after his designs.
In the course of his labours my father’s attention was much given to the question of distinction among lights—a matter of the utmost importance, especially in narrow seas, where many lights are required; and at his suggestion, the Northern Lighthouse Commissioners fitted up a temporary light-tower on Inchkeith, in which numerous experiments having this object in view were made.
Fig. 8. Fig. 9.
He was the inventor of two useful distinctions—the Intermittent and Flashing lights. In the intermittent distinction the light is suddenly obscured by the closing of metallic shades which surround the reflector frame, and on their opening, it is as suddenly revealed to sight, in a manner which completely distinguishes it from the ordinary revolving light, which from darkness, gradually increases in power till it reaches its brightest phase, and then gradually declines until it is again obscured; the action of these shades in producing the intermittent effect is illustrated in [Figs. 8] and [9]. The Flashing light, by a peculiar arrangement of reflectors, and a rapid revolution of the frame which carries them, is made to give a sudden flash of great power, once in five seconds of time, and thus has a distinctive appearance very different from either the revolving or intermittent light. For these distinctions Mr. Stevenson received from the King of the Netherlands a gold medal as a mark of his Majesty’s approbation.
Fig. 10.
Mr. Stevenson also, in 1810, gave a design for a double light at the Isle of May, as shown in [Fig. 10], in which all lighthouse engineers will see the embryo of the double light of the present day.
I must not omit to notice his improvement on the lanterns of floating lightships, now universally adopted, which he introduced in 1807. Previously to this date the lightships exhibited their lights from small lanterns suspended from the yardarms or frames. Mr. Stevenson realised the inutility of such a mode of exhibition, and conceived the idea of forming a lantern to surround the mast of the vessel, and to be capable of being lowered down to the deck to be trimmed, and raised when required to be exhibited. His plan had the advantage of giving a lantern of much greater size, because it encased the mast of the ship, and with this increase of size it enabled larger and more perfect apparatus to be introduced, as well as gearing for working a revolving light. [Fig. 11] shows this lantern, and the following is his description of it:—