In 1873 Professor Tyndall was engaged by Trinity House to conduct a series of experiments on the relative effectiveness of different types of fog signal. South Foreland, with its recently-installed steam power plant, was chosen as the location and a variety of acoustic instruments were set up at the top and bottom of the cliff, to be monitored from a Trinity House vessel offshore. At first three systems were tested: a steam whistle, an air whistle and a pair of air-powered brass trumpets with reeds (designed by Frederick Hale Holmes). Later, other designs of whistle were trialled, as well as a steam 'syren' (provided by Joseph Henry) and three types of gun (operated by gunners from Dover Castle). Tyndall's recommendation was that the siren should provide the standard fog signal at major landfall stations, with reeds judged suitable at some sites; by 1884 sirens were in use at 22 coastal stations and on 16 lightships. Tyndall presented wider conclusions on the acoustic effects of different atmospheric conditions in a paper delivered to the Royal Society the following year.