XXIX.] EXCEPTIONAL PHENOMENA. (;57 



three or four planets approach each other closely, the event 

 is long remembered. A most remarkable conjunction of 

 Mars, Jupiter, iSaturn, and Mercury, which took yjlace in 

 the year 2446 B.C., was adopted by the Chinese Emperor, 

 Chuen Hio, as a new epoch for the chronology of his 

 Empire, though there is some doubt whether the conjunc- 

 tion was really observed, or was calculated from the supposed 

 laws of motion of the planets. It is certain that on the 

 nth November, 1524, the planets Venus, Jupiter, Mars, 

 and Saturn were seen very close together, while Mercury 

 was only distant by about 16° or thirty apparent diameters 

 of the sun, this conjunction being probably the most re- 

 markable which has occurred in historical times. 



Among the perturbations of the planets we find divergent 

 exceptions arising from the peculiar accumulation of effects, 

 as in the case of the long inequality of Jupiter and Saturn 

 (p. 455)- Leverrier has shown that there is one place between 

 the orbits of Mercury and Venus, and another between those 

 of Mars and Jupiter, in either of which, if a small planet 

 happened to exist, it would suffer comparatively immense 

 disturbance in the elements of its orbit. Now between 

 Mars and Jupiter there do occur the minor planets, the 

 orbits of which are in many cases exceptionally divergent.^ 



Under divergent exceptions we might place all or nearly 

 all the instances of substances possessing physical pro- 

 perties in a very high or low degree, which were described 

 in the chapter on Generalisation (p. 607). Quicksilver is 

 divergent among metals as regards its melting point, and 

 potassium and sodium as regards their specific gravities. 

 Monstrous productions and variations, whether in the animal 

 or vegetable kingdoms, should probably be assigned to this 

 class of exceptions. 



It is worthy of notice that even in such a subject as 

 formal logic, divergent exceptions seem to occur, not of 

 course due to chance, but exhibiting in an unusual degree 

 a phenomenon whicli is more or less manifested in all 

 other cases. I pointed out in p. 141 that propositions of 

 the general type A = BC -I- be are capable of expression 

 in six equivalent logical forms, so that they manifest in a 

 higher degi'ec than any other proposition yet discovered 

 the phenomenon of logical equivalence. 



' Grant's History of Physical Astronomy, p iiC\ 



L U 



