surfaces should be oiled with special clock oil. This is applied with a fine wire or broom straw to avoid excess. Sometimes the operation of cleaning may be shortened by washing the clock works in gasoline without disassembling, but this is less satisfactory because it is impossible to thoroughly clean them so.

In watches and small portable clocks, especially the cheap ones, the pendulum and driving weight are replaced by the balance wheel and spiral spring. As a cheap clock might better be thrown away than taken to a clock repairer, it is worth while for the boys of the household to know how to help it along for a little while after it begins to stop. But watches that one values are best not tinkered with by home talent, except to alter the hands and the regulator if the watch runs fast or slow.

Suppose, then, the cheap clock refuses to go, what can the boy tinker do about it? First he takes out the three or four small screws at the back of the case near the edge and lifts out the works. The face and hands come along, too, probably. Take a bowl full of gasoline and cover the works, but not the face, lest it be discolored. Then place the finger gently on one of the little wheels near the escapement and make the clock go a few minutes in gasoline. Then lift out the works and shake them as dry as possible and finish drying them in the air. When fully dry, oil the bearings and the rubbing parts of the escapement with a thin mixture of sewing machine oil and kerosene. If the clock was merely discouraged by thick gummy oil

But very

and dust, this will be treatment enough. likely the balance wheel pivots are worn loose, and hence the balance wheel shaft no longer is at a proper distance from the escapement pinion. This may often be corrected by screwing down slightly at one or both ends the hardened steel cup-ended screws in which the balance wheel pivots turn. Perhaps when this is done the clock will tick unequally. If so, its pinion should be held firmly in pincers and the balance wheel slightly rotated, testing its tick with each adjustment, until the tick is even. If, after all these betterments, the clock still refuses to run-get a new one!

CHAPTER VI

DOORBELLS AND THEIR RELATIVES

THE Algerian Arabs do not need doorbells to announce visitors. They live in walled thatched dugouts with one open doorway and no chimney or windows. At the doorway is tied up a wolfish dog with very sharp teeth and a capacity to bark twenty-nine times every ten seconds for two hours uninterruptedly. His mistress feels quite safe to leave the house in care of her door-keeper. When walking abroad, all Arabs carry sticks to intimidate dogs that might be at large. Anybody who has lived in those countries understands the force of the Bible saying: "Without are the dogs." A lady who visited in an Arab village proposed this conundrum: What is Kadra's door made of? The answer: Dog would bark!

Sometimes we call at a house in our own country where the dog announces our call, but for a very long time it has been thought better form for a guest to announce his own coming. This he used to do by sounding the door with his knuckles. As this might be painful in case the family was far within or hard of hearing, somebody invented a mechanical substitute for the caller's fist. This was the old-fashioned knocker.

Knockers were once nearly universal, and like everything else they soon came to be ornamented. Thus the knockers became fierce lions' or unicorns' heads, or took on still more grotesque shapes.

Picturesquely decorative and effective as the knockers were, they went out of fashion, driven from favor by the mechanical doorbell. It seems strange that a thing so simple, so ornamental, and yet so well adapted to use as the knocker could have been displaced, except in hotels and other places where calls were to be made at great distances, by a thing so much more complicated and more likely to get out of order as the mechanical doorbell. The Darwinian formula for evolution was the survival of the fittest! Here was a case where the fittest was driven out by the less fit. But there was, after all, something prophetic in the coming of the bell and the wire that rung it, for soon the wire was electrified, and the bell came to its own, to stay no doubt forever, owing to its alliance with the electric

current.

But before we come to electricity, consider for a moment how neatly the problem of pulling a bell a great way off was solved mechanically. It was accomplished by a device which will always be known, from association with the doorbell problem, as the bellcrank lever. Imagine a spoked wheel like a wagon wheel to be knocked to pieces till only the hub and two spokes at right angles remain, and let it be mounted on its proper axle, free to be turned. If one pulls on one spoke the other will move, but it moves at right

angles to the direction of the pull. If the two spokes which remain had been at some other angle than a right angle the pull could be changed to some other direction. This is the bell-crank lever principle. As the doorbell-knob was pulled forward, the pull was converted by a bell-crank lever to a vertical direction and passed on by a wire through the floor to the ceiling of the cellar or basement below. Thence a second lever reconverted the direction to the horizontal, and perhaps still another changed it to a new horizontal direction at right angles. So the web of wire and bellcranks was spun along, perhaps through a maze of passages till it reached at length the desired spot where hung the bell upon a spiral spring. Your pull at the door put the spring in vibration here and "jingle-jingle-jingle" spoke the bell.

But maybe the family or the servants had looked out of a window and perceived an unwelcome caller, come to collect a bill, perhaps, or on some ax-grinding expedition. Standing on a chair, they could muffle the bell, and, pull his best and sharpest, the caller could make no sound. Ah! Perhaps here is the secret of the passing of the knocker! Nobody within could stop its unwelcome knock. But for his revenge the caller could pull angrily and yet more angrily, of course, till at length a wire would break and the bell system had to be repaired.

All this is changed with the electric bell. The caller has no resource if the family does not want to receive him. He can push the button till he is weary and