Human nature has a curious tendency, once started in a wrong direction, to continue by inertia until something untoward turns up to modify the tendency or until some definite movement is organized to prevent further progress that may be serious. There are many illustrations of this principle, though perhaps the well-known tendency of the so-called middle C of the musical scale furnishes the best known example. Theoretically this should have 256 double vibrations a second. Instruments were gradually tuned higher and higher, however, making it more and more difficult for the human voice to reach notes that had been reached with comparative ease before, until a definite movement was organized to prevent further heightening and even then the tendency was not entirely overcome. We are in something of the same condition of affairs as regards light as is thus illustrated in sound. When illumination was poor, people went to bed shortly after nightfall and arose at daybreak. As illumination has become better, they have gone to bed later and later, especially in the cities; and the hour of rising has grown later until, in the summer at least, many persons sleep as much during daylight as in the dark.
USING THE DAYLIGHT. JAMA. 2009;302(9):1009. doi:10.1001/jama.2009.1165