The superstitions of old times cling so tenaciously to modern thought that the words "accident" and "chance" commonly connote some mysterious agency. Nothing of the kind is implied here. The word "accident" and the like is used in these pages simply to express the effect of unknown or unnoted causes, without the slightest implication that they are unknowable. In most cases their neglect has been partly due to their individual insignificance, though their combined effect may be very powerful when a multitude work in the same direction. Moreover, a trifling pressure at the right spot suffices to release a hair-trigger and thereby to cause an explosion; similarly, with personal and social events, a trifling accident will sometimes determine a career. Noteworthiness and success may be regarded statistically as the outcome of ability and environment and of nothing else, because the effects of chance tend to be eliminated by statistical treatment. The question then becomes, How far may noteworthiness be accepted as a statistical measure of ability? Ability and environment are each composed of many elements that differ greatly in character. Ability may be especially strong in particular directions as in administration, art, scholarship, or science; it is, nevertheless, so adaptive that an able man has often found his way to the front under more than one great change of circumstance. The force that impels towards noteworthy deeds is an innate disposition in some men, depending less on circumstances than in others. They are like ships that carry an auxiliary steam-power, capable of moving in a dead calm and against adverse winds. Others are like the ordinary sailing ships of the present day--they are stationary in a calm, but can make some way towards their destination under almost any wind. Without a stimulus of some kind these men are idle, but almost any kind of stimulus suffices to set them in action. Others, again, are like Arab dhows, that do little more than drift before the monsoon or other wind; but then they go fast. Environment is a more difficult topic to deal with, because conditions that are helpful to success in one pursuit may be detrimental in another. High social rank and wealth conduce to success in political life, but their distractions and claims clash with quiet investigation. Successes are of the most varied descriptions, but those registered in this book are confined to such as are reputed honourable, and are not obviously due to favour. In attacking the problem it therefore becomes necessary to fix the attention, in the first instance, upon the members of some one large, special profession, as upon artists, leaders in commerce, investigators, scholars, warriors, and so forth, then to divide these into subclasses, until more appears to be lost through paucity of material than is gained through its increasing homogeneity.