The movement of this clock, next to that at Westminster, is the largest in the world, and, in point of quality of material and finish of workmanship, it is unequalled by any. The three main wheels are each two feet in diameter, and cast in the solid, of the very finest gun-metal, the teeth being afterwards cut by an engine made expressly for that purpose. The frame is of the best wrought-iron planed to a smooth surface, and by means of a contrivance, known to engineers as plumber blocks, any part of the mechanism may be removed without disturbing the remainder. The pendulum, which is self-compensating, is over 15 feet long, and vibrates or beats once in two seconds. The quarter chimes, which are struck on four bells, are a modification of those of S. Mary, Cambridge. The great weights necessary to drive so large a clock, and which by the friction they would cause might prejudicially influence its performance, are in this case not allowed to act directly upon the pendulum, but are made to wind up a small auxiliary weight once every half-minute, and this weight imparts an exactly uniform impulse to the pendulum at each vibration. This arrangement, which is called the _remontoir_, is supplemented in this clock by a double lever escapement of a novel kind, in connection with that known as Graham's Dead Beat. A CALENDAR AND WIND-DIAL are useful additions to some edifices. The CALENDAR indicates on special circles of a large dial--by means of three separate hands--the month of the year, the day of the month, and the day of the week. The peculiarity of this invention is that it needs no correction for the long and short months, nor even for the month of February, with its occasional 29 days; as by means of a wheel cut for the successive months in a period of four years, and which takes that time for a single revolution, the calendar is rendered a perpetual one. The mechanism which directs the pointers to the days of the week and of the month is discharged, by the clock, each night at 12 o'clock, when the levers shift the hands to their proper places on their several dials. On the first of the month all three hands on the dial are moved at the same instant.