IN NATURE for April 1 of last year (vol. xi. p. 431) we gave a description of the new Sidereal Standard Clock of the Royal Observatory at Greenwich. Fundamentally important as is this clock in all that concerns its relation to exact astronomical science, it performs also another and more immediately practical duty, that of regulating the time of great part of the United Kingdom. And we propose now to trace the connection existing between this purely astronomical clock and those by which the daily business of our lives is arranged.