xviii.] OBSERVATION. 409 



preserved unless as regards the bones, shells, strong integu- 

 ments, or other hard and durable parts. All the infusoria 

 and animals devoid of mineral framework have probably 

 perished entirely, distilled perhaps into oils. It has been 

 pointed out that the peculiar character of some extinct 

 Horas may be due to the unequal preservation of different 

 families of plants. By various accidents, however, we gain 

 glimpses of a world that is usually lost to us as by 

 insects embedded in amber, the great mammoth preserved 

 in ice, mummies, casts in solid material like that of the 

 Roman soldier at Pompeii, and so forth. 



We should also remember, that just as there may be 

 conjunctions of the heavenly bodies that can have hap- 

 pened only once or twice in the period of history, so re- 

 markable terrestrial conjunctions may take place. Great 

 storms, earthquakes, volcanic eruptions, landslips, floods, 

 irruptions of the sea, may, or rather must, have occurred, 

 events of such unusual magnitude and such extreme rarity 

 that we can neither expect to witness them nor readily 

 to comprehend their effects. It is a great advantage of 

 the study of probabilities, as Laplace himself remarked, to 

 make us mistrust the extent of our knowledge, and pay 

 proper regard to the probability that events would come 

 within the sphere of our observations. 



Apparent Sequence of Events. 



De Morgan has excellently pointed out 1 that there 

 are no less than four modes in which one event may 

 seem to follow or be connected with another, without 

 being really so. These involve mental, sensual, and ex- 

 ternal causes of error, and I will briefly state and illustrate 

 them. 



Instead of A causing B, it may be our perception of A 

 that causes B. Thus it is that prophecies, presentiments, 

 and the devices of sorcery and witchcraft often work their 

 own ends. A man dies on the day which he has always 

 regarded as his last, from his own fears of the day. An 

 incantation effects its purpose, because care is taken to 

 frighten the intended victim, by letting him know his 

 fate. In all such cases the mental condition is the caustj 

 of apparent coincidence. 



1 Essay on Probabilities, Cabinet Cyclopaedia, p. 121, 



