Of course at the last meeting of the Science Club every one wanted to know how we ran a pipe organ by electricity. Moreover the Electrical Show was coming on in the city, and cows were to be milked by electricity, dishes were to be washed by electricity, rugs and furniture were to be cleaned by electricity, and innumerable distracting and distressing things were to take place. I told the boys that really only two kinds of things were to be done by electricity at the show, and if they would give me two one-hour appointments I would furnish them with the key to the whole show. We might as well begin to-day with the pipe organ question. A pipe organ is operated by air. It has bellows which are simply one form of an air pump. A boy is often employed to turn a crank which works the bellows. Down in the basement underneath our pipe organ I will show you how a half-horse-power electric motor takes the place of a boy. We found a dark and dirty corner where a boy used to stand and turn a crank every time æsthetically inclined people enjoyed an organ recital in the room above. Science, which has not been given credit for being _humanitarian_, put an electric motor into that dark corner and sent the boy up stairs to hear the music. The motor _grumbled_ at the dirt in the corner and compelled the janitor to keep it clean. The electric motor, better than any device I know, enforces justice, but never requires mercy, or at least rarely receives it. It comes nearer than any other machine to paying back all that you put into it. It is most economical when working up to its full capacity. I recommend that you look it over carefully and after a few minutes tell me what you have seen in it. [Illustration: Fig. 19] The boys said that it looked just like a dynamo. We must not forget that it is a dynamo, but is here used as a motor by sending an electric current through it. This fact, that a dynamo might be driven by an electric current and serve as a mover of other machinery, was first publicly exhibited in 1873 at the Vienna Exhibition, and by many believed to have been discovered by accident at that exhibit. But why does it look like a dynamo? It has a field whose magnetism is produced by an electric current sent through coils of wire, and it has an armature whose magnetism is likewise produced by the electric current. If it were used as a dynamo, where would it get the electric current to magnetize its field? From its own moving armature. Is it adapted for direct current? Yes. It has a commutator and brushes. Is it shunt- or series-wound? Shunt-wound, as shown by diagram in Fig. 20. [Illustration: Fig. 20]