Springs and their various Structure.--The Elastic Spring.--The Boy’s Catapult and its Powers.--The Pistolograph, its Principle, and Uses to which it can be put.--Leaf-rolling Caterpillars, and their Way of Work.--The Carriage Spring.--The Horse’s Hoof and its complex Structure.--Fungi and their united Power.--The Chinese Cross-bow.--The ancient Balista.--Skull of the Crocodile.--Bones of young Children.--The Spiral Spring and its many Uses.--The Toy-gun.--The Needle-gun.--Valved Brass Instruments.--Watch and Clock Springs.--The Bed Spring.--Parallels in Nature and Art.--Buffers of Railway Carriages.--Spring Solitaires.--The Bell Spring.--Spiral Springs in Vegetable Tissues.--Poison Cells of various Marine Animals.--Effects of the Spiral Springs. ELASTIC SPRINGS. Here we come upon a subject so large, that it is difficult to define its exact requisite limits. The principle of the elastic spring pervades all Nature, and the numerous adaptations in Art are closely, though perhaps not directly, attributable to the wide distribution of the spring in Nature. There is, for example, the simple elasticity which enables a tree, when bowed by the wind, to spring back so soon as the pressure is removed, and which, indeed, is the power which enables a bow to propel an arrow. Then there are spiral springs innumerable, many of them so minute that they can only be seen by the aid of the microscope, and there are many springs which exhibit their elasticity by their power of extension and shortening, just as is done with the elastic fabrics which are so much in vogue at the present day, and which seem so necessary to ordinary comfort that we feel disposed to wonder how our forefathers managed without them. We will now proceed to examine some of these springs in detail. * * * * * THERE is one form of elastic spring which has of late years become more familiar than agreeable, namely, the toy which is learnedly called a “catapult,” though it has little in common with the ancient weapon whose name it bears. As may be seen by reference to the illustration, it consists of one or more india-rubber straps attached to a fork-like handle, and carrying a small pouch in which is contained the missile. Although it is not remarkable for accuracy, it can throw a stone or a bullet a considerable distance, and its power can be very quickly increased by adding to the number of the straps. Thus a catapult has been made which was capable of sending a small pistol bullet through a wooden board, so that the child’s toy might really become a dangerous weapon. Indeed, cases are known where the catapult has hurled a stone with fatal effect upon human beings. In my own neighbourhood there are many examples of glass being pierced by stones thrown from catapults just as if they had been subjected to bullets shot from firearms, the holes being quite small and round.