conducted on the lines he initiated. Under his superintendence no fewer than twenty lighthouses were designed and constructed, and many improvements, now in universal use, were due to his ingenuity. He brought the catoptric or reflecting system of lighting to perfection, advocated the adoption of the dioptric or refracting system with its central lamp, and invented the intermittent and flashing lights; for the last invention the king of the Netherlands bestowed on him a gold medal. The most important of his lighthouses was the famous Bell Rock tower, erected on a dangerous reef submerged by every tide to the depth of twelve feet, and lying in the fairway of ships making for the estuaries of the Tay and Forth. Previous attempts made by Captain Brodie to erect beacons upon it had failed. In the storm of 1799 seventy sail were wrecked off the reef, among them the York, 74-gun ship. After a careful survey Stevenson designed and modelled a tower, and reported on 23 Dec. 1800 to his board that the erection of a stone tower on the reef was practicable. Public opinion was sceptical, and when the board applied to parliament in 1803 for powers to carry out the design, the bill after passing the commons was withdrawn owing to difference of opinion regarding the extent of coast over which dues to meet the expense of erection and maintenance should be levied. Before again going to parliament the board, on Stevenson's suggestion, consulted John Rennie [q. v.], who concurred in Stevenson's opinion. Both Stevenson and Rennie gave evidence before a new parliamentary committee, and the act was passed on 21 July 1806. Active operations were begun on the reef in August 1807. Rennie was appointed nominally chief or consulting engineer, to whom Stevenson in any case of difficulty could apply. Rennie, who had no experience of lighthouse construction, suggested various alterations of the design, but to none of them Stevenson gave effect. After five years of arduous labour the lighthouse was in working order. Stevenson described its construction in 1824 in his ‘Account of the Bell Rock Lighthouse.’ The tower, which, as in all Stevenson's lighthouses, is free from architectural adornment, rises to the height of 100 ft.; the diameter at the base is 42 ft., diminishing to 15 ft. at the top. Above the solid, which is 30 ft. in height, is the entrance doorway, the interior being divided into six stories. Smeaton in his Eddystone tower adopted an arched form of floor, rendering it necessary to insert chains embedded in the masonry to counteract the outward thrust; but in the Bell Rock tower, by an ingenious arrangement of the masonry, the stone floors were converted into effective ‘bonds,’ thus tying the walls together, for as the stone floors form part of the walls, outward thrust is prevented. All subsequent rock towers have this form of floor. The cubic contents of the tower are more than double those of the Eddystone, from which it differs in many respects owing to its far more difficult and dangerous site. The tower was protected both externally and internally from lightning stroke, and thirty-five years afterwards, on the advice of Faraday, a somewhat similar arrangement was applied to the Eddystone tower. The optical apparatus consisted of parabolic reflectors of silvered copper, combined with argand burners, arranged on a four-sided frame, the best and most complete apparatus then known; and, as a means of further distinguishing the light, it was made to show red and white alternately, hence Sir Walter Scott's ‘ruddy gem of changeful light.’ Since the lighting of the Bell Rock not a single wreck has taken place on the reef. The Northern lighthouse board directed a bust of Stevenson, by Samuel Joseph, to be placed in the tower, and at his death placed in their minutes their regret at the loss of him ‘to whom is due the honour of conceiving and executing the great work of the Bell Rock Lighthouse.’
Not only was the tower itself novel in design, but the implements used in its erection had to be invented. The balance and movable jib cranes were for the first time used at the Bell Rock. The latter is now in universal use. Ball-bearings were also introduced into the cranes at the Bell Rock for the first time. Stevenson further designed for the temporary lightship moored off the Bell Rock tower during its construction—the first lightship placed in so deep water—a lantern to surround the mast, instead of small lanterns hung from the yard-arms or frames. This improvement is now universally adopted.
In 1814 Sir Walter Scott made his celebrated voyage round Scotland with Stevenson and the lighthouse commissioners, starting from Leith on 29 July and reaching Greenock on 8 Sept. On 30 July he visited the Bell Rock, and inscribed some appreciative lines in the lighthouse album. Speaking of Stevenson in his journal, he says: ‘The official chief of the expedition is Mr. Stevenson the surveyor—viceroy over the commissioners—a most gentlemanlike and modest man, and well known by his scientific skill.’
Stevenson's practice was not confined to
