At the present time the tube is used for commercial purposes and for
passenger traffic. Air tight cars of special design are used, and only
one car is allowed in the tube at one time.

[Illustration: The Gravity-Car of Holen.]

You cannot imagine the frightful velocity of the ride, but the passenger
is not as conscious of this as you might think. The first fifty miles of
the descent is controlled by the exterior or surface engines. The speed
is gradually increased until it reaches that of the falling body. Then
the motorman releases the wizard car and the speed is steady and
terrible until the car dashes past the center of gravity, after which
the speed slackens at a regular rate. The car of its own momentum forces
its way far toward the opposite surface of their earth.

Just as the carriage comes to a stop, the engineer or motorman, as we
would call him, pulls his lever, thereby fastening the car to the ribbed
side of the tube. At once a signal is given and the long, thin but
strong rope descends to draw the carriage to the surface.

A perfect system of communication is established from one end of the
ponderous tube to the other. It frequently happens when an attempt is
made to fasten the car that the clamps fail to work and consequently the
carriage commences its second journey toward the center. Another effort
is made to hold the carriage when it again comes to a stop; but if this
is not successful, then comes the most peculiar experience of all. The
carriage of its own momentum continues dashing backward and forward
until it comes to rest at the center of gravity. Then the engineer, by
communicating with the surface, gets the longest stretch of rope and is