(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 neighbours privacy. A builds a house in the town near Bs 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 As house which are ordinarily excluded from observation, and B acquires a like easement with respect to As house.
