The larger number of vessels are, however, loaded from the "straiths." These are platforms placed over the river and connected with tramways, joined to the various pits.  The waggons, each containing two and a half tons of coal, come down for many miles until they reach the "straith," when they are brought to a stand.  In the "straith" is a hatchway, which opens by machinery, through which the waggon descends with a man in it, who, when it arrives over the hold, unfastens a catch which secures the bottom of the waggon; this being made to turn upon hinges, like a trap door when opened, the whole of the coal is poured into the hold. Attached to the suspending machinery are two counterpoising weights, which being less heavy than the waggon laden with coal, do not impede its descent.  The moment it is discharged of its coal it is drawn up again by these weights.