A year is, roughly speaking, the period which it takes the earth to perform one complete revolution round the sun. I say "roughly speaking" with due humility, having the fear of the expert ever before my eyes, because I know that if I do not sing small, that inconvenient person, the astronomical critic, will come down upon me at once like a wolf on the fold, with minute distinctions about the mean, the tropical, and the sidereal year; matters of immense importance at Greenwich Observatory, no doubt, but elsewhere of very little interest indeed, seeing that they differ from one another by so many minutes only. Let us leave the astronomers their own problems. The year with which I am going to deal humbly here is a much more commonplace, ordinary, and comprehensible year--the visible year of vegetation, of plant and animal life, of the four seasons; the year as roughly known to children and savages, and to the weeds, the flowers, the bees, and the squirrels. It has often struck me as curious that people took this complex concept of the year so much for granted--inquired so little into its origin and discovery. Yet it is by no means everywhere obvious. How did men first come to notice, in the tropics especially, that there was such a thing as the year at all? How did they first observe, save in our frozen north, any fixed sequence or order in the succession of Nature? How did they learn, even here, that spring would infallibly follow winter, and summer be succeeded in due course by autumn? And, to go a step farther back, how did the plants and animals, in all parts of the world alike, come originally to discover and adapt themselves to all these things? How did the bee know that she must "gather honey all the day from every opening flower," the summer through, in order to use it up as bodily fuel in winter? How did the plants learn when to blossom and produce seed? In one word, how did the seasons come to be automatically recognized? That they _are_ automatically recognized, even by plants, quite apart from the stimulus of heat or cold, drought or rain, a single fact (out of many like it) will sufficiently prove. Trees brought from Australia to England, where the seasons are reversed, try for two or three years to put forth leaves and flowers in October or November--the southern spring. It takes them several autumns before they learn that the year has been turned upside down--that June is now summer and December winter. This shows that life moves in regular cycles, adapted to the seasons, but not directly dependent upon them. The rhythm of the world has set up an organic rhythm which now spontaneously and automatically follows it.