The electric time-ball, erected on the Calton Hill last October by the Government, and placed under the author's charge, has now been at work for five months. But the work has necessarily been of an experimental or tentative character; for before the accuracy of the signals could be guaranteed, it was necessary to have experience of the machinery in all weathers; and, moreover, the present strength of the Observatory establishment, and the nature of pre-existing occupations, prevented the experiments being made every day.