72 
THE TELEGRAPH. 
first was, on its arrival, supposed to be the second, and so on ; 
throughout part of the day the messages received were not 
those that were expected, until at length a comparison of 
memoranda indicated the nature of this singular accident. 
3. Carriers jammed together in opposite directions. —Oases 
of this kind are similar to that described in the first example. 
4. Breakage of the piston. —The collar is attached to the piston 
by means of a screw, which one day in winter having broken off*, 
the train stopped, and became frozen up in the tube. It was 
a difficult matter to open the tube, for the line went under a 
bridge, and the river being frozen over, a floating scaffold could 
not be used. Several pistons were filled with hot water and 
were shot into the blocked part. They gradually removed the 
obstacle, and arrived at the end of the tube with the carriers 
and some lumps of ice. The screw still remained in the tube, 
but by sending on another piston very slowly, it also was pushed 
out. 
5. Accident to the tube. —When the tube has been laid in 
trenches, the ground may be disturbed in laying gas or water 
pipes, or during the repairing of the pavement, and then the 
tube may receive a stroke from a pickaxe, which, though not 
penetrating it, may flatten it. This, of course, causes the 
stoppage of the carriers. Leakages of the air, which it might 
be expected would be frequent, are on the contrary unknown, 
even in cases where the tubes are exposed to the oscillations of 
the roadway of a bridge. 
6. Trials of neiv carriers. It might be supposed that a piston 
fitted on its external surface with what is practically a brush 
would effectually carry out of the tube all the dust and mud it 
might contain. Unfortunately, whatever the brush carries 
away it takes to some lower or narrower part of the tube, when, 
after a few passages, it sticks itself so firmly that it is impossible 
to urge it on by pressure. 
How the Service is carried on during a derange¬ 
ment.— While efforts are being made to send forward the 
stopped despatches, those that should follow must not be de¬ 
layed, and the following rules are adopted in such cases:— 
While trials and examinations are being made on the 
deranged portion of the line between any two offices, a service 
of carriages is established through the streets by which the 
