But no such implication can be raised under the provisions of this will The gift over is not on an indefinite failure of issue to the daughter, but on such failure in the lifetime of the husband. The intent of the testator is expressly declared to be, not for the benefit of the issue of the children, but to exclude their father from inheriting the estate from them. Upon his death, their estates are to become absolute, and if they should die in his lifetime, leaving issue, the estate would descend to such issue in fee. The description of the contingency, therefore, upon which the gift over is to take effect, is such that it must be construed to be an executory devise. The gift to the children was of a fee; it cannot be cut down to an estate-tail by implication; there can be no remainder after the gift of a fee; it is the limitation of a fee on a contingency after a previous estate in fee, and must take effect, if at all, as an executory devise. The heirs-at-law of the testator, to whom the estates are devised upon the happening of the contingency, if they do not take by descent, must claim as executory devisees.

But it is urged, that the limitation being to the heirs-at-law of the testator, the estate must vest in them by descent, and that they cannot take as purchasers under the will. This argument is founded on the well settled rule of law, that a devise to an heir, of the same estate in nature and quality as that to which he would be entitled by descent, is void. In such cases, the heir takes by descent and not as purchaser. Ellis v. Page, 7 Cush. 161, and cases there cited. • If this rule applies to the present case, then it would follow that the gift over to the heirs-at-law would fail as an executory devise, so that their title would not depend upon the principles of law by which estates of that nature are governed.

But it is entirely clear that this devise over to the heirs of the testator does not come within the recognized tests by which an heir is held to be in by descent, and not by purchase. It is essential to a title by descent that the heir should take the same estate in quantity and quality, as if no will had been made and the estate had been left to descend to him; and this rule is not affected by carving out of the fee a prior particular or contingent estate, or subjecting it to an executory devise. All that is necessary to the operation of the rule is, that when the estate vests in the heirs, they should hold it by the same tenure and in like manner as if the devise had been omitted. If the nature or quality of the estate is changed when it comes to the heirs, of if they take it in different shares or proportions, the descent will be broken, and they must come in as purchasers under the will. Ellis v. Page, 7 Cush. 164; Reading v. Roys-ton, 1 Salk. 242, 2 Ld. Raym. 829, and 1 Com. R. 123; 6 Cruise Dig. tit. 38 c. S, §§9, 10.

Applying this rule to the present case, it is clear that the heirs-at-la\v of the testator must take as devisees, and not by descent. The limitation over to them is contingent until the prescribed event shall occur. The devise is to those who shall be his heirs when the contingency arises, and not to those who were his heirs at the time of his decease. They must take the estate under and by force of the will, in such proportions as it may vest in them when the event occurs, and not as heirs-at-law in the shares to which they would have been entitled if the devise over to them had been omitted. Such, we think, was clearly the intent of the testator. The rules of construction, that the word "heirs" in a will is usually construed to mean those who are such at the time of the testator's decease; and that estates created by devise are to be held to be vested rather than contingent; must give way to the controlling rule of interpre-. tation that the intent of the testator is to govern, if it does not conflict with the rules of law. Cholmondeley v. Clinton, 2 Jac. & Walk. 70, 80, 89; Doe v. Frost, 3 B. & Ald. 546; Richardson v. Wheatland 7 Met. 169; Olney v. Hull, 21 Pick. 314. And if it be found to conflict, it does not change the rule of construction. The will must fail of effect so far as to violate the rules of law, not because the intent of the testator does not control its construction, but because the law will not permit his intent to be accomplished. Brattle Square Church v. Grant, 3 Gray, 158; Hall v. Priest, 6 Gray, 22, 23.

The intent of the testator, in making the limitation to his heirs-at-law in this clause of the will, is not left in any doubt. It is expressly declared, to be to prevent his son-in-law from inheriting any portion of the testator's estate, as heir to his children. The devise to the heirs was to take effect only upon one contingency. If the child survived the father, or died in his lifetime, leaving issue, the heirs-at-law were to take nothing. The object of the testator was, not to benefit his heirs, but to break the legal course of descent in a certain contingency, so as to exclude his son-in-law from participating in his estate, beyond the specific sum bequeathed to him.

To carry out this intent, it is necessary to construe the limitation to heirs, as being to those who should hold that relation when the contemplated contingency should happen. If it should be held to mean a devise to the heirs of the testator at the time of his decease, this declared purpose would be defeated. The right or possibility of taking the estate in the prescribed contingency, would then have vested in part in the testator's daughter, at his decease, as one of his heirs; on her death, her share or proportion of this right or possibility would have descended to her children; and, in case of their death, without issue, in the lifetime of their father, it would go by descent to him - the very result which the testator sought most sedulously to prevent by this limitation to his heirs. It cannot be supposed that the testator intended to make a provision, the effect of which would be to admit his son-in-law to a share in that part of his estate, from which he expressly declared it to be his purpose to exclude him.