Mankind has had idols ever since consciousness began. Advancing knowledge has changed the nature and number of the idols, but it has not destroyed them. The idol of the present age is “Science,” and men worship it in the degree that it seems to fit their needs. They forget that Science is merely the knowledge of things and persons, arranged and classified, so as to make it available. In its nature it is fallible, for some new phase discovered to-day may show that yesterday’s conclusion was formed from a theory which itself was based on a mistaken premise. Man has caught a glimpse of something that resembled truth, has stated it, reasoned about it, and finally either established its authority or disproved it utterly through the discovery of the real thing he was seeking. Either result was progress, because man grows, as Browning says, “through catching at mistake as midway help, till he reach fact indeed.” So there is no need to be disturbed by the conflicting opinions of men of science touching the purpose or method of sleep. Even the rejected theories have added to the sum of our knowledge, and the field for investigation is still open to all who are faithful in noting and comparing the manifestations of Nature, which the scientists call phenomena. Most of what we call science has to do with physical or material things. Consequently, we find scientists dealing mainly with what may be called tangible phenomena, those which may be measured or weighed or held in the hand or, at least, pinned down by pressure of thumb or finger. Material Science’s estimate of man is largely gauged by “Things done, that took the eye and had the price; O’er which, from level stand, The low world laid its hand, Found straightway to its mind, could value in a trice.” This is the almost inevitable result of looking upon life as purely material or physical. We must view life as physical, but not physical only; as mental, but not mental only; as spiritual, but not spiritual only. In studying sleep and its attendant phenomena all these things must be taken into consideration. So slight a thing as fancy may profoundly influence our acts; fancies not attributable to any material source, so fleeting and evanescent that the clumsy net of language cannot hold them, may induce sleep or destroy sleep. A review of the theories and conclusions of physicians, both scientific and unscientific, as well as of others who have found the study of sleep of absorbing importance, will find a place in our examination of this vital function of organisms. CHAPTER II HOW MUCH SLEEP Six hours in sleep, in law’s grave study six, Four spend in prayer, the rest on Nature fix. (Translation.) SIR EDWARD COKE.