The saw-mill was not attached as personal estate by leaving a copy of the writ at the dwelling-house of the town-clerk (Scott v. Manchester Print Works, 44 N.H. 507), and there was no attempt to levy an execution upon it as a chattel. If the plaintiff acquired any title in the property by the extent of the execution, it was by virtue of an attachment of real estate. At the time of the attachment, the mill was not annexed to the realty. It was agreed that Locke might erect the mill there for the purpose of manufacturing the lumber. So far it was a mere license to build a saw-mill upon the land, and, by the license, the mill did not become real estate. The agreement of the other parties to the contract to buy the mill or sell the land at their option did not operate to annex the mill to the land (Ashmun v. Williams, 8 Pick. 402), nor give Locke an interest in it which could be attached as real estate.

At that time Locke had no right to receive a conveyance of the land. Whatever right he had under the contract was not of the nature of a present interest in real estate. There was no vested interest. It depended upon a double contingency, — a contingency upon a contingency. It was only a right to acquire the right to compel the owners of the land to make the alternative election to buy his mill or sell to him their land. He could not claim a conveyance until the owners of the land should exercise the option *Page 106 of buying or selling, and the option was not to be exercised until Locke should perform his part of the contract by cutting and manufacturing the lumber. If they could, on refusal, be compelled in equity to exercise the option, it could not be done until Locke should perform his agreement. If he had so far performed as to be able to compel an election, that election might be to take instead of to give a conveyance. And if the plaintiff would be equitably entitled to the proceeds of the sale, in case of an election to buy the mill, the fund could not be reached by an attachment and the extent of an execution such as were made in this case.

The right of Locke was a personal one, and could not without the consent of the other parties be transferred to a third person. The right to compel an election that he should take or give a conveyance depended upon a condition precedent, and that condition could only be performed by Locke personally. It could not be satisfied by the payment of money. The power to compel an election to buy or sell might never come into existence, for Locke might refuse to perform the conditions, and their performance could not be compelled. The duty of performing the conditions was not assignable, and the right depending upon the performance of the duty could not be assigned. Bethlehem, v. Annis, 40 N.H. 34; Rollins v. Riley, 44 N.H. 9. There being no present right to a conveyance of the land, nor right to compel an election to buy or sell, and whatever right existed, from its dependence upon personal services not yet performed, not being assignable, there was no attachable interest of Locke's in the land at the time of the attachment.

The subsequent sale of the land to Locke was not an exercise of the option provided for by the contract, and the right of Locke in the land acquired by purchase subsequent to the attachment. could not be affected by the attachment. It was only Locke's interest, at the time, that was attached and subsequently taken by execution. The interest acquired by Locke subsequent to the attachment did not accrue to the plaintiff by way of estoppel, as in case of after acquired interests of the grantor following covenants of title. Crocker v. Pierce, 31 Me. 177; Drake Att., ss. 223, 234, 245. Without the right subsequently to be acquired by performance of the condition, the right at the time of the attachment was not an attachable interest in the land. The plaintiff could not perform the condition and make perfect the right, and he acquired no lien by his attachment, and, as against the defendants, took nothing by the levy of his execution.

Case discharged.

STANLEY, J., did not sit: the others concurred. *Page 107