but slackens speed, and prepares to stop at the home signal. He must, however, on no account pass either home or starting if they are at danger. In short, the distant merely warns the driver of what he may expect at the home. To prevent damage if a driver should overrun the home, it has been laid down that no train shall be allowed to pass the starting signal of one box unless the line is clear to a point at least a quarter of a mile beyond the home of the next box. That point is called the standard clearing point.
Technically described, a block is a length of line between the last stop signal worked from one signal-box and the first stop signal worked from the next signal-box in advance.
INTERLOCKING SIGNALS.
A signalman cannot lower or restore his signals to their normal positions in any order he likes. He is compelled to lower them as follows:—Starting and home; then distant. And restore them—distant; then starting and home. If a signalman were quite independent, he might, after the passage of a train, restore the home or starting, but forget all about the distant, so that the next train, which he wants to stop, would dash past the distant without warning and have to pull up suddenly when the home came in sight. But by a mechanical arrangement he is prevented from restoring the home or starting until the distant is at danger; and, vice versâ, he cannot lower the last until the other two are off. This mechanism is called locking gear.
LOOKING GEAR.
There are many different types of locking gear in use. It is impossible to describe them all, or even to give particulars of an elaborate locking-frame of