Our brass instruments would be very badly off without the spiral spring, which is placed under the pistons. The elasticity allows the pistons to be pressed down, and when the fingers are raised the pistons spring up again.
Another form of this instrument is seen on the right of the ordinary spring. This is used in the manufacture of spring mattresses and couches, and is made thinner in the centre, so as to allow of greater elasticity.
Below them is the spring which is used for watches and clocks, one end being fastened to the rim of the barrel, and the other to the pivot. When the latter is turned the spring becomes “wound up,” and, when released, keeps the works going by pressing against them. Of the “pall-and-ratchet” wheel, by which the movements are retarded, we shall treat in another place.
On the left hand of the illustration are a few figures of the Spiral Spring as seen in Nature.
On the extreme left of the group is a spiral cell taken from the flower-stem of the Water-lily. As the reader will see, it is composed of a number of fibres laid parallel to each other, and twisted into a hollow spiral. In order to exhibit its shape the better, the spiral has been partially uncoiled.
On the extreme right is a corresponding spiral cell from the common Lily, in which the spring power is given by two fibres twisted in opposite directions. The reader will now understand and admire the mechanism by which these plants attain their great strength and elasticity, the stems being made of myriads of these spiral fibres.
The oval body on the upper part of the illustration is a poison-cell of a marine polyp, and is given here as an example of an animal spiral spring, the others all belonging to the vegetable world.
We shall see more of its structure a little further on, and will not now examine it in detail.
The two remaining figures represent the remarkable objects called Antherozoids, i.e. the living creatures of anthers. They exist in vast numbers in the non-flowering plants, and inhabit those parts which correspond with the anthers of the flowering plants. When placed in water they have a curious way of coiling and twisting themselves spirally, so as to make their way through the water in a tortuous, but tolerably rapid, course. This movement is effected by the contraction and expansion of the spirally twisted filament. The upper figure represents a group of Antherozoids in their cells, and the lower is a much more magnified figure of a single Antherozoid as it appears when free, and in the act of moving through the water.
On the accompanying illustration are many examples of Spiral Springs, both natural and artificial. We will take these in their order.