This volume, while it is complete in itself, is also the first of a trilogy, the scope of which is suggested in the prologue. The story of scientific discovery has its own epic unity-a unity of purpose and endeavour-the single torch passing from hand to hand through the centuries; and the great moments of science when, after long labour, the pioneers saw their accumulated facts falling into a significant order-sometimes in the form of a law that revolutionised the whole world of thought-have an intense human interest, and belong essentially to the creative imagination of poetry. It is with...