the incidents of property, or it may be an easement. The easement of light and air is a continuous easement and negative easement. The owner of land can take and use for his own property as much light and air as come within the boundaries of his land, but the quantity of light and air available for his use is, in a large measure, dependent upon act of his neighbour. So if his neighbour, in the free enjoyment of his own property, erect buildings thereon in such manner as to diminish the flow of light and air on to the other's land, the latter would have no redress unless he could show a right on his part precluding his neighbour from erecting such buildings. Such a right if it existed would clearly be restrictive of the other's right to enjoy his property as he pleased, and could only arise as an easement. An easement of light and air is the purely legal right that servient owner shall not, by any act on the servient tenement, diminish the quantity of light and air to which the dominant owner is entitled.