ORRERY. This name has been applied to four different kinds of machines for repre senting the phenomena of the solar system. A planetarium exhibits the orbital motion of the planets about the sun ; a tellurian and lunarian, when combined, exhibit, respectively, the motion of the earth about the sun, and of the moon about the earth; and a satellite machine exhibits the motion of Jupiter's satel lites about their primary. Planetary machines were in use at a very remote period, and appear to have consisted for many centuries of moveable spheres having the earth in their centre. In the 17th century Huyghens and Roemer employed themselves in the construc tion of planetary machines in conformity with the Copernican doctrine. Roemer also in vented a satellite machine prior to the year 1679. In England, about the year 1700, Mr. George Graham constructed a machine which exhibited the motion of the earth about the sun, while the 'moon revolved about the earth ; one of these machines was made for the Earl of Orrery, from which circumstance the term Orrery originated. A large planeta rium was, in 1801, made for the Royal Insti tution of London, and a more complete instru ment was constructed by Dr. Pearson in 1813.
To produce the revolution of the planetary bodies about the sun, a system of vertical con centric tubes is usually employed, which are adjusted very near to each other, but yet so far removed as not to influence each other's motion. These tubes are of different lengths,
the innermost being the longest, and to the superior extremity of each a radius or pro jecting wire is attached, and thereby made to revolve once during each revolution of the tube. The lower extremities of the tubes form the arbors or axes of as many toothed-wheels, which are either immediately driven by pin ions adjusted to a verticlo axle called the " annual arbor," or derive their motions indi rectly from those pinions by means of an interposed train of wheels. The determin ation of the relative number of teeth Which must be givers to the wheels and pinions, in order to produce the required motion, depends upon the relative YeloCitief bf the niotibir to be imitated; and heie the machinist. /Mist depend Upon the astronomer. As an hid to astronomi cal orreries are lest highly estimated than they formerly were. . .
0811R is the name given to various Species of Salix Or Willow, employed in basket making on account of their tough , flexible shoots. [BASKET-Mlitrxe WILLOW.]