VOLVELLES 15 



tarium, 3! inches in diameter, the period of about 1433-60, is in MS. 

 Digby4 8 > f. 113- 



Peter Apiari a made such a model on a larger scale, by which he 

 represented the epicyclical motions of the planets by means of movable 

 circles of cardboard of various colours, and expected by such means 

 to be able to find their positions without computation. This model 

 interested the Landgrave Wilhelm IV of Hesse so greatly that he had 

 circles of copper made for the same purpose. He found considerable 

 errors in existing star catalogues, and became convinced of the 

 necessity of making systematic observations. With Tycho he redeter- 

 mined the position of Spica virginis. 



Something of the same kind may be seen in the wonderful instru- 

 ment book, MS. Savile 100, which is, so far- as we know, as yet 

 undescribed. 



The splendid folio work of I. P. Gallucius, Speculum uram'cum, 1593, 

 is illustrated with very numerous volvelle, one for each of the planets. 



ASTRONOMICAL MODELS 



78. Globe. Gilt brass on Stand. c. 1700. 

 Diameter 5^ inches. Orrery Coll. 10. 

 I. Rowley fecit. 



79. 2^-inch Globe set to turn in a brass meridian divided in degrees. 



c. 1700. 

 Orrery Coll. 24. 



80. i^-inch Globe of Ivory on a Stand. c. 1700. 



Orrery Coll. 25. 



81 A pair of wire Planetaria. c. 1700. 



Diameter 15! inches. Orrery Coll. i. 



1. Ptolemaic Planetarium. 



2. Copernican Planetarium. 



82. A pair of Planetaria mounted within Armillary Spheres. 



c. 1700. 



Diameter 14 inches. Orrery Coll. 7. 



On Stands, Brass : Scales silvered. 



1. Ptolemaic. 



John Rowley Londini fecit. 



2. Copernican. 



I. Rowley fecit. 



1 Peter Apian's Astronomicum Caesareum 1540, a large book dedicated to 

 Charles V. 



