Locomotion.—Direct Action.
The second point which has to be elucidated is that or progress by means of Direct Action.
We have already seen how vessels can be propelled by sail, oar, paddle, or screw. We have now to consider a mode of progress which requires none of these things, but which works by means of Direct Action.
Such, for example, is the progress of a Rocket through the air.
The heated gases rush out with tremendous violence, and, by their pressure, urge the heavy rocket into the air with the rush, roar, and bang so familiar to all who have witnessed a good display of fireworks.
A rocket in the act of ascent is shown in the uppermost figure of the accompanying illustration.
Below it is shown the Water Turbine, the principle of which is evident from the sketch.
From each of the apertures a stream of water is forcibly directed, and, by its resistance, spins the vessel round and round. There are several shops in London in which this instrument may be seen at work.
Although in such positions it is necessarily a mere toy, it carries with it, in common with many other toys, the germs of valuable inventions. Indeed, there have been attempts to utilise the principle of Direct Action in the propulsion of vessels, but as yet the mechanical difficulties have proved practically insuperable, and, although a vessel has been thus propelled, the expense has been heavier than that of the paddle or screw, and the speed not nearly so great.
On the right hand of the illustration is another example of Direct Action, called the Electric Tourniquet.
In the two previously mentioned instruments the motive power is visible, but in this it is invisible except in the dark.
The principle is exactly the same as in the pocket or water tourniquet; but, instead of heated air or a stream of water, electricity is used. The instrument is attached to an electric machine, and fully charged. The electric fluid rushes out of the points, forces itself against the air, and so, by its recoil, drives the machine round and round upon its pivot.
We will now take two examples of Direct Action as found in Nature.
Perhaps many of my readers have seen the Octopus, and admired the manner in which it glides through the water, trailing its long arms behind it. Whence the force comes is not easily seen, and the creature appears to move almost by volition. In reality, however, it employs Direct Action. It takes water into the body, and then it ejects it through a tube called the “siphon” with such force that the animal is propelled backwards through the water.
Some of the creatures belonging to the Cuttles, and popularly called Squids, can use such extraordinary powers that they can project themselves far out of the water. In consequence of this power, they are sometimes called Flying Squids, and, as they have been known to shoot themselves completely over the hull of a large ship, they well deserve the name.
The common Squid of our coasts, which furnishes the so-called Cuttle-bone, affords us a good example of Direct Action. I once hatched a number of young Squids from the grape-like eggs, and it was most curious to see how the little creatures shot about as soon as they escaped from the egg.
They also utilised the siphon in another way. Poising themselves just above the sand with which the bottom of the vessel was covered, they directed a stream of water upon it, and thus formed little cavities into which they settled like birds into their nests.
The figure represents the Paper Nautilus as it appears while passing through the water. Just at the base of the tentacles is seen the short siphon, from which it is pouring the stream of water which drives it along.
Below the Nautilus is seen the larva of the common Dragonfly. We have, when treating of the Lazy-tongs, already described the mode in which the insect takes its prey, and our object could not be served by repetition. Suffice it to say that the insect is shown in the act of ejecting water, and so shooting itself along in preparation for seizing prey.