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new works and advise on developments such as changes to the lenses or fuel sources. The other would deal with the ordinary business of the lights, such as inspection tours, preparing accounts, buying stores and managing the keepers. The division, he argued, would strip the engineer’s department of non-engineering work, since much of the work they were currently responsible for did not require any form of technical expertise. As he pointed out, the Board of Trade’s insistence on picking over the NLB accounts with a fine tooth comb had created enough work to support another full-time employee. Finally, he noted that ‘should the Board see fit to entrust the New Works to the charge of my brother and myself…we should use every endeavour to urge them on as vigorously as possible.’ Other contractors, he noted delicately, were simply not as good as the Stevensons. He and Tom knew the lights like no one else. When other engineers had been hired, their performance ‘lead[s] us to anticipate that we could conduct the works much more expeditiously than perhaps under any other arrangement which the Board could make’. After due consideration, the Commissioners approved the idea and appointed a separate General Manager to help with the bureaucracy of the service.

From then on, therefore, David and Tom were free to return to the purer details of planning new lights. Between 1854 and 1880, the two were responsible for the construction of twenty-nine lights around the coast, from Butt of Lewis and MacArthur’s Head to Ushenish, Monach, Skurdyness and Lochindaal. Commissions were also beginning to come in from abroad. Foreign governments, encouraged by the reputation of the NLB and the gathering fame of the Stevensons’ achievements, looked to the Scottish lights as their templates. Tom and David were asked to supply lights first for the Indian government and then for Japan, Canada and Singapore. The commissions were lucrative but daunting. Until then, they had been accustomed to working with purely local conditions – freezing waters, Atlantic ferocity, hurricane-force gales, everything that a sullen northern climate could fling at them. But they did not have experience of the problems that came with designing lights for earthquake zones and tropical temperatures. In a high Indian summer, for instance, the lights could overheat, the lantern glass crack and the lead melt. Japan, on the other hand, had a similar climate to Scotland, but had to take account of fault lines and earthquakes. The East also had its share of other problems. The waters of China and Malaya supported a thriving population of pirates and wreckers who responded predictably to the threat to their trade. In several cases, the Malayan lights had to be encased in so much protective lead that the cost of defending them far exceeded the cost of constructing them. The engineers working on the Malacca Straits lights had to be armed at all times to defend themselves against the wreckers, and even the keepers were forced to carry guns. In practice, however, the years of experience in Scotland had provided the Stevensons with almost all the knowledge they needed to build a lighthouse almost anywhere in the world. Dovetailing stone blocks provided flexibility during tremors, thickened glass withstood monsoon rains, and iron lights built on stilts (similar to the rocket-shaped barracks at the Bell Rock and Skerryvore) could be used for sandbanks or wreckers’ territory.

Tom, meanwhile, was preoccupied with lenses. His dioptric holophotal light was an adaptation of Fresnel’s earlier work, but instead of using a set of fanned mirrors above the lens to drive the light outwards (as Alan had chosen for Skerryvore), it enclosed the light in a prismatic glass casing. The popular image of a lighthouse lens (an immense convex apparatus with thick myopic portholes in the centre, topped and tailed with angled prisms) was, in part, Tom’s lasting contribution to optics. The new dioptric holophotal light (holophotal meaning ‘whole light’ in Greek) finally dispensed with the need for reflectors, and