18. An easement may be acquired in virtue of a local custom. Such easements are called customary easements.Illustrations(a) By the custom of a certain village every cultivator of village land is entitled, as such, to graze his cattle on the common pasture. A, having become the tenant of a plot of uncultivated land in the village, breaks up and cultivates that plot. He thereby acquires an easement to graze his cattle in accordance with the custom.(b) By the custom of a certain town no owner or occupier of a house can open a new window therein so as substantially to invade his neighbour's privacy. A builds a house in the town near B's house. A thereupon acquires an easement that B shall not open new windows in his house so as to command a view of the portions of A's house which are ordinarily excluded from observation, and B acquires a like easement with respect to A's house.