128 
THE TELEGRAPH. 
a free passage for waggons (fig. 70). The wires should, how¬ 
ever, not be made to cross highways unless it is absolutely 
necessary. 
When there is a large number of wires, it is better to put 
up a second line on the unoccupied side of the road, instead of 
unduly increasing the height of the posts on one side. 
This is really cheaper and safer ; for when the posts have to 
carry a large number of wires, they are more liable to be thrown 
Fig. 70. 
down, and their fall often completely stops the working of the 
line. When there is a double line of posts, such an accident 
could happen only under circumstances quite exceptional. 
Posts 30 feet high are only used separately, or for short 
distances, or, for instance, within stations where the wires pass 
over many sets of rails, or where several lines branch off. 
They are separately used in ordinary telegraph lines wherever 
there is any important crossing. 
Posts 24 feet high and 21 inches girth at 2 yards from the 
