EXCEPTIONAL PHENOMENA. 323 



by the Chinese Emperor, Chuen Hio, as a new epoch for 

 the chronology of that Empire, though there is some 

 doubt whether the conjunction was really observed or was 

 calculated from the supposed laws of motion of the planets. 

 It is certain that on the i ith 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 remarkable which has occurred in his- 

 torical times. 



Among the perturbations of the planetary motions we 

 may find divergent exceptions arising from the peculiar 

 accumulation or intensification of effects, as in the case of 

 the long inequality of Jupiter and Saturn (vol. ii. p. 70). 

 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^. 



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 which is more or less manifested in all other 

 cases. I pointed out in p. 162 of the first volume, that 

 propositions of the general type A = B C + be are capable 

 of expression in six equivalent logical forms, so that they 

 manifest in a higher degree than any other proposition 

 yet discovered, the phenomenon of logical equivalency. 



Under the head of divergent exceptions we might 

 doubtless place all or nearly all of the instances of sub- 

 stances possessing physical properties in a very high or 

 low degree, which were described in the chapter on 



S Grant's ' History of Physical Astronomy/ p. .116. 

 Y 2 



