Rugg, C. J.
The plaintiff, being the owner in fee of certain open land next to the Old South Meeting House on Washington Street in Boston and the predecessors in trust of the defendants being the owners of an adjacent large office building then in process of construction and since completed, made an indenture by which the plaintiff granted to the trustees for a term of years “an easement of uninterrupted light and air over the premises hereinafter described above the level of the grass plot on the northerly side of the tower of the Old South Meeting House and the right to project over not exceeding five feet of said premises” with cornices and other things. A stipulated rental was reserved to be paid “without any reduction on account of any future taking of part of the above mentioned premises by the city of Boston or other public authority for any purpose, . . . but if the whole of the premises over which the said easements are hereby extended, or the major part thereof, is taken by the city of Boston or other public authority, or if the substantial enjoyment of the easements hereby created be impaired either by any structure placed on any portion of said premises taken by the city or other public authority pursuant to and in connection with such taking or otherwise,” then there should be a reasonable reduction in the rent. The premises were described by metes and bounds and distances as in ordinary conveyances.
Thereafter a taking was made by the transit commission for the city of Boston. It was not in any aspect the talcing of an entire fee of the premises. Treating the earth and air above it as a solid, it was the taking of a series of prisms or prismatic sections which varied in vertical thickness between the extremes of fifty feet and twenty-four and one tenth feet. Described with reference to the surface of the earth in the open space, over which the easement extended, the highest plane of any prism was ten feet above it and the lowest not over forty feet below it. The right to suitable support for the prisms and structures which might be placed within them, by soil or otherwise, was taken *216below the lower planes of the prisms; otherwise, that below was left to the plaintiff. To the plaintiff as owner was definitely reserved the exclusive use of all areas above the upper planes of the prisms. Certain rights of support and of use for various purposes in common with the public use were preserved to the plaintiff.
The total area of land made subject to the easement of light and air in favor of the defendants’ building was two thousand one hundred and fifty-six square feet. Of this, as a result of the taking, the city had exclusive surface rights in approximately four hundred and fifty-seven square feet and there remained to the plaintiff exclusive surface rights in four hundred and seventy-one square feet. Over the remaining surface of one thousand two hundred and twenty-eight square feet a right of way, as foot passages, was taken and the plaintiff retained the right of use in common with the public. It has not been argued that the form of taking is not in accordance with the statute or is unconstitutional. Boston v. Talbot, 206 Mass. 82.
It is not now contended that there has been any substantial interference with the enjoyment of the defendants’ easement. The finding of the Superior Court is conclusive against such a contention. An examination of the evidences discloses no reason to disturb this finding. Jennings v. Demmon, 194 Mass. 108. The controversy is whether “the major part” of “the premises” over which the easement extends has been taken. “Premises” is a word which may have different meanings dependent upon its connection and the object to which it is applied. It oftentimes describes the fee of land. But it may signify something less extensive, if the context seems to require it.
In order to determine the sense in which it was used in this indenture, it is important to bear in mind the subject about which the parties were contracting and their general purpose. The predecessors of the defendants as trustees were constructing a large office building with stores on the street floor in the congested part of Boston. The thing secured to them by the indenture *217was an easement of light and air over a tract of land on one side of their building. There was in contemplation of the parties the possibility that the ownership in fee of the plaintiff in the ■servient estate might-be lessened by some exercise of the power of eminent domain. The indenture is dated December 20, 1902, while St. 1902, c. 534, authorizing the Washington Street subway, was approved on June 27, 1902. The parties provided for the contingency of a taking under the authority of this statute. The first point settled by their contract was that there should be no reduction of rent simply if a part of the plaintiff’s premises was taken, nor if any part should be conveyed or released for the widening of Washington Street and all claim for compensation by reason of any such taking, release or conveyance by the trustees against the public authorities was assigned to the plaintiff. This plainly indicates that the parties contemplated only a practical easement of light and air and that a theoretically legal, or other impairment of the easement, should work no change in their respective rights and obligations under the indenture, and that as to the public the plaintiff should represent the entire fee. The agreement then proceeds to deal with a fair adjustment between themselves of their respective rights and obligations in the event of disturbance of their contractual relations by an exercise of eminent domain. It is obvious that in touching this subject in this connection the parties contemplated a situation which would in fact make less valuable the easement, and thus equitably require a reduction of the rent reserved. They were not providing a means of revising their contract as to rent for any other reason. There is to be a reduction of rent if the substantial enjoyment of the easements is impaired by the erection of any structure or otherwise by the public authority. This protects the trustees in the event of any actual damage to them arising from the physical exercise of public rights. In that connection occurs the further stipulation (now under consideration) “if the whole of the premises over which the said easements are hereby extended, or the major part thereof, is taken.” There was some claim in the trial below that this meant major part in value. But that proposition is not urged now. It is argued, however, that as the public has rights in the larger portion of the surface area of the premises, a major part of them has been taken. But the taking *218of rights in the whole of the superficial area for pedestrian travel alone cannot reasonably be held in this connection to be a taking of the major part of the premises. The taking provided against is one which would give to the public authorities a right at any time to do, upon the whole or a major part of the premises, acts which might interfere with the easement. The natural meaning of the words is an absolute taking in fee of more than'half the premises as measured on the surface of the earth. But perhaps the words go further here and may include a taking even though less than of a fee which would authorize constructions over a larger part of the surface area extending high enough to interfere with the easement. But where the right taken in no case extends more than ten feet above the surface of the earth, and this only for a small area, and over the rest of the area a right of travel for people on foot is taken, it cannot be said, having reference to the circumstances attendant upon the making of the contract, that a major part of the whole premises is taken. Under other conditions and where a different thing was the subject of the contract a different result might be reached. But where parties are contracting about an easement of light and áir over valuable land in the heart of a great city,- which may be used profitably many feet above and below the surface of the earth, the surface area does not appear to be the measure by which to gouge the whole or major part of the premises. This construction gives a practical meaning to the agreement. Where the public acquire in the larger part of the premises rights, the exercise of which may interfere with the easement reserved, then the prospect of harm might be found to render the easement instantly less valuable, even though there was no immediate change in fact. The apprehension of the possible utilization of the right acquired might affect the character of tenants and the value of rentals. If the right was taken in less than the major part of the premises, then only an actual impairment in the substantial enjoyment of the easement would warrant a reduction of rent. Any other interpretation produces a result wide of any connection between a practical interference with the easement of light and air which was the subject about which the parties were making their agreement, and a demand for reduction in the annual rental.
There is not much weight in the argument that the instru*219ment of taking was in effect a taking of the entire premises and that the rights remaining in the plaintiff were granted to it as new rights. The ultimate result accomplished by the exercise of the single act of eminent domain is the substance of the matter.
Decree affirmed with costs.