ation ever moved to her from complainants for the privilege of constructing said windows. Mrs. Theiss also filed a cross-bill, in which she alleged that the wall contemplated by the party-wall agreement was to be a solid wall throughout its length and height; that without her consent, and contrary to her wishes, complainants had constructed windows in it and had encroached upon her property, by the window sills, shutters, and the hinges upon which the shutters were hung, extending out over her property; also that the party wall for the second and third stories was so constructed by complainants that she was deprived of the use of three inches of her property. The cross-bill further alleged that the stairway and other obstructions at the rear of complainants' property were in violation of her right to the use of said alley in accordance with the terms of the agreement between the parties. The cross-bill prayed that the original complainants be required to close up the windows and restore the party wall to a solid wall, remove the window sills, hinges and shutters, also the stairway in the alley, and to pay cross-complainant damages for the use of three inches of her second and third stories. Answer and replication were filed to the cross-bill and the cause was heard before the chancellor on both the original and crossbills. There was no evidence to support the allegations of the original bill that Mrs. Theiss had made a verbal agreement with complainants by which they were authorized to place windows in the party wall, and complainants filed an amended bill, which was substantially like the original bill except that it did not allege the windows were constructed by virtue of any agreement, but alleged the windows were placed in the wall with the knowledge, approval, acquiescence and consent of Mrs. Theiss and under circumstances which now estop her from insisting that they be closed.

The decree found that the windows were constructed with the knowledge, consent and acquiescence of Mrs. Theiss and she was estopped from objecting to their re

maining in the wall. She was perpetually enjoined from closing the window openings, also from closing the air-shaft on her side of the wall, and from doing any act which will interfere with the free use, for all purposes, of the windows opening into the air-shaft. The decree ordered that the sills at the bottom of the windows opening into the airshaft remain as they now are, but that complainants remove the stairway at the rear of their building and the iron shutters and hinges to the windows opening into the air-shaft, and that complainants pay Mrs. Theiss $75 as the amount equitably due her for placing the second and third stories of the party wall three inches further upon her property than was proper. This appeal is prosecuted by Mrs. Theiss.

By her assignment of errors appellant questions the correctness of that part of the decree enjoining the closing up of the windows and the removal of the projecting sills, and the closing of the air-shaft on her property if she sees fit to close it. Complainants have by cross-errors questioned the correctness of the decree requiring the removal of the stairway, the iron shutters and hinges upon the windows opening into the air-shaft, and also the requirement that complainants pay Mrs. Theiss $75 on account of the second and third stories party wall having been built three inches farther over on Mrs. Theiss' property than it should have been.

Appellees seek to sustain the decree upon two theories: (1) That the parties by their acts interpreted the contract as authorizing the construction of windows in the party wall; and (2) that appellant is estopped now from objecting to the windows and from closing or requiring them to be closed. In our view neither of these positions is tenable. The rule that courts will look to the interpretation placed upon a written contract by the parties to it in construing the instrument, only applies where from the ambiguity of words used a doubt arises as to the proper meaning of the writing. In such cases courts will look to the acts of

the parties for aid in construction. (Burgess v. Badger, 124 Ill. 288; People v. Murphy, 119 id. 159; Railroad Co. v. Trimble, 10 Wall. 367.) There is no ambiguity in the party-wall agreement before us. It required a solid wall throughout its entire length and height. Kuh v. O'Reilly, 261 Ill. 437; Springer v. Darlington, 207 id. 238.

We are furthermore of opinion that there was an entire failure of evidence to show any claim on the part of appellees, or any recognition on the part of appellant, that the windows were placed in the wall by virtue of any right or authority conferred by the party-wall agreement. In their original bill complainants claimed the windows were constructed by virtue of a verbal agreement, but this position. was abandoned and in their amended bill they do not claim they were constructed by virtue of any agreement whatever. They do allege appellant knew of and acquiesced in their construction, but it is not now claimed that her consent to their construction was ever procured or asked. The windows were placed in the wall and the obstructions complained of built in clear violation of the written agreement, and if appellant is now barred from insisting upon the windows being closed and the obstructions removed it could only be upon the ground of an equitable estoppel, and this is what is mainly insisted upon by appellees.

The principal facts are, that in the winter of 1909-10 appellees erected a two-story building on their lot adjoining that of appellant, and in doing so built the party wall one story higher. They constructed seven windows in the wall overlooking the roof of appellant's building. In 191112 they built a third story and constructed two windows in the third-story party wall overlooking appellant's property. It does not appear that appellant made any complaint about these windows at that time. In September, 1912, appellant commenced the construction of a second and third story to her building for the residence of herself and husband, and in doing so she left an air-shaft or opening for light and

ventilation next to the party wall, about twelve feet square, from the top of the first story up through the roof, and thereupon, without consulting appellant, appellees closed all the windows in the party wall except one which opened into the air-shaft and constructed four others opening into the air-shaft, two in the second story and two in the third,at a cost, as we understand the proof, of $123. Appellant objected to the maintenance of the windows in the party wall, and in March, 1913, she notified appellees, in writing, to close them, whereupon this suit was begun.

We do not think the case presents any of the elements necessary to the application of the doctrine of equitable estoppel. There is a total lack of proof that appellees constructed the windows in the wall by virtue of any claimed right they had, under the written agreement or otherwise. It is not sufficient, to raise an estoppel against appellant, that she knew the windows were placed in the wall and did not object or take steps to prevent it at the time they were constructed. Appellees were not acting in ignorance of any of the facts. They knew a solid wall was contemplated by the agreement throughout its length and height, and must be presumed to have known that in putting the windows in the wall they were acting in violation of the agreement and were invading the rights of appellant. In order to claim the benefits of an equitable estoppel the party setting it up must have acted in ignorance that the state of facts upon which he claims to have relied was not the true state of facts. The only basis for the claim of estoppel against appellant is that she made no protest at the time the windows were put in the wall. It would be carrying the doctrine of equitable estoppel farther than it has ever been carried in any case we know of, to hold that appellant is barred from insisting that the wall be maintained in accordance with the written agreement. The purpose of placing and maintaining the windows in the wall originated with appellees, with

out any claim of right upon which to base the purpose and without any statement, acts or conduct of appellant to mislead or deceive them. Her mere failure to object to the violation of her right at the time of the invasion, under such circumstances could not, upon any equitable grounds, give appellees a perpetual right to enjoy the fruits of their wrongful act. Appellees were not ignorant of any facts but were as cognizant of them as appellant. There was no element of fraud on the part of appellant. "There must be deception, and change of conduct in consequence, in order to estop a party from showing the truth." (Davidson v. Young, 38 Ill. 145.) In Mullaney v. Duffy, 145 Ill. 559, it was said where it is sought to establish an estoppel from the silence of a party who in equity and good conscience should have spoken, it is essential that the party sought to be estopped should have had knowledge of the facts and the other party have been ignorant of the truth and have been misled into doing that which he would not have done but for such silence. The rule was stated in Holcomb v. Boynton, 151 Ill. 294, as follows: "As we understand the doctrine of estoppel in pais, it is based upon a fraudulent purpose and a fraudulent result. Before it can be invoked to the aid of a litigant it must appear that the person against whom it is invoked has by his words or conduct caused him to believe in the existence of a certain state of things and induced him to act upon that belief. If both parties are equally cognizant of the facts and one has acted under a mistaken idea of the law, the other party cannot say he has been deceived thereby and is entitled to an application of the rule, but will be considered as having acted upon his own judgment, solely. The essential elements are, misrepresentation or concealment of material facts, ignorance of the truth of the matter by the party to whom the representations were made, and reliance upon his part in acting upon the representations.-2 Story's Eq. Jur. 1543;