1878.] of Astronomical Tables. 153 



Albategnius, the most celebrated of all Arab astronomers (ixth 

 century), speaks only of cainit and cauda lunae without the di^a- 

 conis. 



Alfraganus, another Arab astronomer living about the same 

 time, uses the expressions caput and cauda draconis. 



The expression "eighth sphere" is all but, though not actu- 

 ally employed in .the classical authors. It occurs first, as far as 

 I am aware, in the Tiniceus of Plato, p. 36, in a passage of which 

 the following is a translation, modelled on that by Mr Jowett: 

 "This entire compound, i.e. the matter of the cosmical system, 

 he divided lengthways into two parts, which he joined to one 

 another at the centre like the letter ^t and bent them into a 

 circular form, connecting them with themselves and with each 

 other at the point opposite to the point of contact : he then 

 imparted to each a motion centred" upon one and the same point, 

 placing one of the circles in the interior, the other on the exterior. 

 The exterior motion he styled the motion of the Nature of the 

 Same : the interior motion, he styled that of the Nature of the 

 Different. .^ ^ ^ To the Nature of the Same and the Like he 

 gave dominion, for that he left it single and undivided : but the 

 innerjnotion he split six times into seven unequal orbits, having 

 their intervals in the ratios of two and three, i.e. three intervals 

 of each ; and bade their orbits move in opposite directions among 

 themselves, three moving at a uniform velocity, and the remaining 

 four at velocities differing among themselves and different to that 

 of the three, but still not irregula.r." 



At p. 38 of the same treatise, we have mention of the Morning 

 Star, i.e. Venus, and Mercury, but the other planets have no 

 names assigned to them. 



The same views are expressed however by Cicero, and with 

 more simplicity, Tusc. Disp. v. 24. " Quum totius mundi motus 

 conversionesque perspexerit, szc?eraque viderit innumerabilia ccelo 

 inhmrentia cum ejus ipsius motu congruere, certis infixa sedibus : 

 septem alia suos qusque tenere cursus," and better still in the 

 doubtful Somnium Scipionis : " Novem orbibus vel potius globis 

 connexa sunt omnia : quorum unus est cselestis, extimus : ^ ^ ^ in 

 quo infixi sunt illi qui volvuntur stellarum cursus sempiterni ; cui 

 subject! sunt septem, qui versantur retro, contrario motu atque 

 coelum." The Sun, Moon, and five planets are then enumerated ; 

 the paragraph ending, " Nam ea quae est media et nona, Tellus, 

 neque movetur, et infima est, et in eam feruntur omnia suo 

 nutu pond era." 



It will be easily understood that a theory sanctioned by such 

 high authorities as Plato and Cicero, retained its position until a 

 very late period, and it will be found practically recognized by 

 Goclenius, Physica completa, Lib. iii. cap. ii. ed. 1604, by Mo- 



