In all vital phenomena there is periodicity. The barometer comes to its minimum height for the day between four and five in the evening; again, it is at its maximum height between eight and ten in the morning and between eight and ten in the evening. The two first of these periods is when the electric tension is at its minimum; at its maximum during the two latter periods. The basic unit of the lunar day is twelve hours. An ordinary or solar day is two days, and an ordinary week is two weeks. This hebdomadal or heptal cycle governs, either in its multiple or submultiple, an immense number of phenomena in animal life in which the number seven has a prominent place. A Mr. Hay, of Edinburgh, writing some sixty years ago, says: "There is harmony of numbers in all nature--in the force of gravity, in the planetary movements, in the laws of heat, light, electricity and chemical affinity, in the forms of animals and plants, in the perceptions of the mind. Indeed, the direction of natural and physical science is towards a generalisation which shall express the fundamental laws of all by one simple numerical ratio. The mysticism of Pythagoras was vague only to the unlettered. It was a system of philosophy founded on existing mathematics which comprised more of the philosophy of numbers than our present." Philosophical students of human nature have taken note of the danger professional and business men encounter when they extend their mental activities beyond the hour of four p.m. (by the sun). Thousands fail because of their ignorance of the fundamental laws governing all things physical. The morning hours up to ten a.m. are just as dangerous for many who are highly susceptible to the electric tension which occurs up to that hour. The feeling that prevails from four to eight in the afternoon is one of mental or physical fatigue, that in the morning one of irritability. Lincoln was not immune from natural law. On one occasion, at five p.m., he was suddenly informed of the defeat of the Northern Forces, and it was feared by those who were present that he would fall to the ground. Mr. C. C. Coffin sprang forward to assist the President, who, however, succeeded in returning to the White House unaided. Nature creates the natural, man the unnatural. Solomon declared: "To everything there is a season, and a time to every purpose." _Lincoln's Face_ Knowledge, conviction, and certainty gave to Lincoln's face that penetrating power which could not have been assumed on occasion even by the most versatile and gifted actor. The two following quotations from "The Valley of Shadows" describe Lincoln's personal appearance and the emotions produced by the expression of his features:-- "'The sperrit air more in the eye than it air in the tongue,' said Elihu Gest, rising from his seat; 'if Abe Lincoln looked at the wust slave-driver long enough Satan would give up every time.'