Lighthouses are striking totems of our relationship to the sea. For many, they encapsulate a romantic vision of solitary homes amongst the waves, but their original purpose was much more utilitarian than that. Today we still depend upon their guiding lights for the safe passage of ships. Nowhere is this truer than in the rock lighthouses of Great Britain and Ireland which form a ring of 19 towers built between 1811-1905, so-called because they were...