Part 27 (1/2)

[Illustration: FIG 215--The bolt of a Barron lock]

THE CHUBB LOCK

is an amplification of this principle It usually has several tu 216 The lock stud in these locks projects froh which the stud must pass as the lock moves, are cut in the tumblers It will be noticed that the forward notch of the tue with similar serrations in the bolt stud and ins tokey is inserted

[Illustration: FIG 216--Tuht steps That nearest the head (8) operates a circular revolving curtain, which prevents the introduction of picking tools when a key is inserted and partly turned, as the key slot in the curtain is no longer opposite that in the lock Step 1 moves the bolt

[Illustration: FIG 217--A Chubb key]

In order to shoot the bolt the height of the key steps must be so proportioned to the depth of their tuates in the tuht level for the stud to pass through the 218 Here you will observe that the tuht (lifted by step 2 of the key) has a stud, D S, projecting from it over the other tumblers This is called the _detector tu tool is inserted it is certain to raise one of the tumblers too far The detector is then over-lifted by the stud D S, and a spring catch falls into a notch at the rear It is now impossible to pick the lock, as the detector can be released only by the right key shooting the bolt a little further in the locking direction, when a projection on the rear of the bolt lifts the catch and allows the tumbler to fall The detector also shows that the lock has been taht key cannothas been perfor all the tuht]

Each tuiven one of thirty different heights; the bolt step one of twenty Bythe order of the steps in a six-step key it is possible to get 720 different cohts the possible combinations may be raised to the enormous total of 7,776,000!

[Illustration: FIG 219--Section of a Yale lock]

THE YALE LOCK,

which comes from America, works on a quite different system Its most noticeable feature is that it perh the number of combinations possible is still enors 219, 220, 221) we show theof the key The keyhole is a narroisted slot in the face of a cylinder, G (Fig 219), which revolves inside a larger fixed cylinder, F As the key is pushed in, the notches in its upper edge raise up the pins A1, B1, C1, D1, E1, until their tops exactly reach the surface of G, which can now be revolved by the key in Fig 220, and work the bolt through the mediu key is inserted, either some of the lower pins will project upwards into the fixed cylinder F (see Fig 221), or some of the pins in F will sink into G It is then impossible to turn the key

[Illustration: FIG 220--Yale key turning]

There are other well-known locks, such as those invented by Bramah and Hobbs But as these do not lend themselves readily to illustration no detailed account can be given We ht, however, notice the _time_ lock, which is set to a certain hour, and can be opened by the right key or a number of keys in combination only when that hour is reached

Another very interesting device is the _automatic combination_ lock

This may have twenty or more keys, any one of which can lock it; but the same one must be used to _un_lock it, as the key automatically sets the mechanism in favour of itself With such a lock it would be possible to have a different key for every day in thehands it would be useless unless it happened to be the one which last locked the lock

[Illustration: FIG 221--The wrong key inserted The pins do not allow the lock to be turned]

THE CYCLE

There are a few features of this useful and in some onderful contrivance which should be noticed First,

THE GEARING OF A CYCLE

To a good eared to 70 inches,” or 65, or 80, as the case ear the faster one ought to be able to travel Let us therefore exa farther

The safety cycle is always ”geared up”--that is, one turn of the pedals will turn the rear wheelspeed we count the teeth on the big chain-wheel, and the teeth on the small chain-wheel attached to the hub of the rear wheel, and divide the former by the latter To take an example:--The teeth are 75 and 30 in number respectively; the ratio of speed therefore = 75/30 = 5/2 = 2-1/2 One turn of the pedal turns the rear wheel 2-1/2 ti this result by the diameter of the rear wheel in inches Thus a 28-inch wheel would in this case give a gear of 2-1/2 28 = 70 inches

One turn of the pedals on a ear would propel the rider as far as if he were on a high ”ordinary” with the pedals attached directly to a wheel 70 inches in dia the number ratio of the teeth on the two chain-wheels If for the 30-tooth wheel we substituted one of 25 teeth the gearing would be--

75/25 28 inches = 84 inches

A handy for = T/_t_ D, where T = teeth on large chain-wheel; _t_ = teeth on s-wheel in inches