Nature's teachings : human invention anticipated by nature / by J.G. Wood.

  • John George Wood
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: Nature's teachings : human invention anticipated by nature / by J.G. Wood. Source: Wellcome Collection.

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    windows of workshops. Perhaps its revolution may not assist the air-current, but it does, at all events, show how much exhausted air has to be expelled from the room, and conse- quently how much fresh air needs to be brought into it. Perhaps the reader may be surprised to see that the Wings and Tail of a bird and a boy's Kite are placed among the exam]3les of the Spiral principle. Yet such is the fact. If the reader will move up and down the wings of any bird which will not bite him, he will find that there is in them a peculiar screwing motion, difficult of description, but very observable. It is mostly for want of this movement that all our attempts at fitting wings to human beings have been such utter failures. We can make the wings work up and down well enough, but we cannot as yet impart to them the all-important spiral movement. That very well-known toy, the Kite, is another example of the same principle which drives the screw steamer. Its tail, which need be nothing but a piece of string with a propor- tionate weight at the end, keeps the Kite in a slanting posi- tion, providing that the belly-band be properly arranged. The consequence is that the pressure of the wind acts on it as on a wedge, and so drives it upwards until the combined weight of itself and the string counterbalance the upward pressure. Indeed, the only object of the string is to keep the Kite at a proper inclination; and, if that object could be attained by the force of gravity alone, the Kite would ascend to a height nearly double that to which it can at present attain. Centrifugal Force. Closely connected with the spiral principle is Centrifugal Force, that marvellous power which gives to our whole solar system its ceaseless movements, and may extend, as far as we know, to other and vaster systems yet unknown. Tie a ball to a string, and swing it round, and it wiU be an exact, though rough, representation of the double power by which the movements of the heavenly bodies are governed, our earth being included among them.