656 THE PRINCIPLES OP SCIENCE. [CHAP. 



They are not anomalous but only extreme events, analogous 

 to extreme runs of luck. There seems, indeed, to Be a 

 fallacious impression in the minds of many persons, that 

 the theory of probabilities necessitates uniformity in the 

 happening of events, so that in the same space of time there 

 will always be nearly the same number of railway accidents 

 and murders. Buckle has superficially remarked upon the 

 constancy of such events as ascertained by Quetelet, and 

 some of his readers acquire the false notion that there is a 

 mysterious inexorable law producing uniformity in human 

 affairs. But nothing can be more opposed to the teachings 

 of the theory of probability, which always contemplates the 

 occurrence of unusual runs of luck. That theory shows 

 the great improbability that the number of railway accidents 

 per month should be always equal, or nearly so. The 

 public attention is strongly attracted to any unusual con- 

 junction of events, and there is a fallacious tendency to 

 suppose that such conjunction must be due to a peculiar 

 new cause coming into operation. Unless it can be clearly 

 shown that such unusual conjunctions occur more frequently 

 than they should do according to the theory of probabilities, 

 we should regard them as merely divergent exceptions. 



Eclipses and remarkable conjunctions of the heavenly 

 bodies may also be regarded as results of ordinary laws 

 which nevertheless appear to break the regular course of 

 nature, and never fail to excite surprise. Such events vary 

 greatly in frequency. One or other of the satellites of 

 Jupiter is eclipsed almost every day, but the simultaneous 

 eclipse of three satellites can only take place, according to 

 the calculations of Wargentin, after the lapse of 1,317,900 

 years. The relations of the four satellites are so remarkable; 

 that it is actually impossible, according to the theory of 

 gravity, that they should all suffer eclipse simultaneously. 

 But it may happen that while some of the satellites are 

 really eclipsed by entering Jupiter's shadow, the others are 

 either occulted or rendered invisible by passing over his 

 disk. Thus on four occasions, in 1681, 1802, 1826, and 

 1843, Jupiter has been witnessed in the singular condition 

 of being apparently deprived of satellites. A close con- 

 junction of two planets always excites admiration, though 

 such conjunctions must occur at intervals in the ordinary 

 course of their motions. We cannot wonder that when 



