The faster you rub the sooner you get the fire. It is not at all easy to make the fire because it is not easy to rub fast enough; but a meteor rushes into the air at a great speed, fifty miles a second at least. It seems to us a great speed when our motor-car goes at 50 miles an hour; think what it must be to go at 50 miles a second, nearly 4000 times as fast as a motor-car! I am afraid the police would not allow us to try it; but if we could increase the speed more and
Fig. 21.
more, we should find that the air which at first gently blows us cool, was becoming a fierce wind; and presently, instead of being at all cool, it would seem hot; and long before we reached the speed of a meteor t would be unbearable.
It may seem surprising that anything so soft and thin as air can produce the same effect by friction as we get from hard wood, but we can actually prove it by experiment. Sir James Dewar devised this ingenious apparatus to do so (Fig. 21). A wooden arm AB can be spun about the end A. The end B thus rushes at a considerable speed through the air not the speed of a meteor, or anything like it, but still a sufficient speed to be heated by friction. The heating will not be very great, but I think we can detect
