We think that the ancients, if they had seriously reflected upon the important part played by the sun in the economy of nature; how it is the heart, and spring, and inner power of every movement and manifestation of life; how it is, as Sir David Brewster says, the centre and soul of our world, the lamp that lights it, the fire that heats it, the magnet that guides and controls it, the fountain of colour, which gives its azure to the sky, its verdure to the fields, its rainbow-hues to the gay world of flowers, and the purple light of love to the marble cheek of youth and beauty;--we think that the ancients, if they had thought upon, or had known, all this, would not have given the earth a chief place in our system. And that they did so is all the more strange when we remember that they attributed to the world a _soul_ (the "soul of the world" is a favourite idea with the great philosophers of antiquity), and looked upon the planets as living creatures. But they were swayed by that egotistical instinct which leads man to refer everything to himself, even the very gods which he has created after his own image. The Bible teaches us that there is but one God. Alas! are there not as many gods as there are men? Does not each of us create a deity in accordance with his own inclinations, his mode of thought, his degree of mental culture, the sphere of his ideas? Is the God of a tolerant philosopher identical with that of a bigoted fanatic? It is not so much due to a deceitful appearance, an optical illusion, as to a kind of innate infatuation, that the human race have come to consider the planet they inhabit as the centre of the universe. CAUSES OF THE CIRCULATION OF THE SAP. Let us return to the sap, the life-blood of vegetation. How is it that its movement does not recommence at the same time in all plants? Why are some clothed with leaves when the others are scarcely budding? Wherefore, in certain genera, do the flowers appear before the leaves? Some authorities assert,--but facts show it to be a purely gratuitous supposition,--that the flower, which, with the fruit, seems to be the goal or object of vegetation, demands a greater activity on the part of the sap. But, in truth, many trees and shrubs, such as the poplar, the willow, and the hazel, flourish at an epoch when the sap is barely aroused from its protracted lethargy. These are questions which have still to be answered. But upon yet another question we may dwell at some detail. What is the cause of the circulation of the sap?