In 1876 Tyndall was again engaged to make a comparative study at South Foreland, this time of two different types of electric generator: the magneto and the dynamo. (In 1869 Holmes had speculatively constructed a pair of dynamos and suggested them for the permanent South Foreland installation, but at the time they were not considered sufficiently tried and tested.) The trial took place over the winter of 1876-77, and the dynamo was demonstrated to be both mechanically and electrically superior. A set of Siemens dynamos was shortly afterwards installed at Lizard Lighthouse when it was converted to electrical operation in 1878.