It was Washington's birthday. The schools were to have a holiday and the Science Club was to hold a special, open meeting at which I had been asked to present the subject of electricity in the household. I replied to the programme committee that that was too large a subject, but that I would talk upon electric heating. I warned them, however, that it would be a dry study, and not an entertainment. They replied that the father of his country had been born at a time of the year when the weather was unfavourable to outdoor sports, and that February usually found them acclimated to vigorous study. Neither they nor their friends objected to study if it seemed to have a motive. I found an audience composed of old and young, men and women, girls and boys. Most of them had left school--many of them because their teachers thought they were incompetent to continue. [Illustration: Fig. 65] Not far from here is "a wheel in the middle of a wheel ... as for their rings they are so high that they are dreadful ... and the spirit of the living creature is in the wheels." Those wheels are now sending the electric current to this room for our experiments. I propose to show that we convert electricity into heat by offering resistance to its flow. Experience teaches us that resistance to motion always produces heat. At Niagara Falls thousands of tons of water descend at the rate of one hundred and sixty feet in three seconds. When the water reaches the bottom of the falls, it is moving a little faster than a mile a minute. The resistance which this mass meets after its fall retards its motion and generates heat. Hundreds of meteors fall into our atmosphere daily, travelling a thousand times as fast as the waters of Niagara Falls. The resistance to their motion, which our atmosphere offers, heats them white hot, melts them, vaporizes them, burns them up, so that very few of them reach the solid earth in a solid condition. An iron spile driver, measuring two cubic feet, weighs about half a ton. When it falls sixteen feet upon the end of a spile it is moving at the rate of twenty miles an hour. The energy of this moving mass depends upon both its weight and its velocity, and when its motion is arrested by the spile that energy of motion is largely converted into heat energy, from which both the spile and the spile driver get hot. A piece of iron may be made red hot by pounding it with a trip hammer. Count Rumford found, in 1798, while boring cannon in the arsenal at Munich, that the resistance which the iron offered to the motion of the boring tool furnished heat enough to boil water. Seven hundred and seventy-eight foot pounds of mechanical energy when converted into heat would raise one pound of water (one pint) one degree. This is called the British thermal unit. The spile driver, weighing 1000 pounds, falling 16 feet upon a spile, produces heat enough to raise 1 pint of water 20 degrees. [Illustration: Fig. 66]