The opinion of the Court was' delivered by

— The objection to the survey of the streets of Manayunk, as confirmed by the Quarter Sessions, is, that the committee appointed by the Burgess and Council performed a part of their duty at one time, and the remainder at another. If the case stood upon the footing of an ordinary power of appointment or revocation, the law is, that the power need not be executed to the utmost extent at once, but may be executed at different times over different parts of the estate: 1 Sugd. on Powers 357. But the ease does not rest solely on this ground. By the Act of 13th July, 1842, the committee appointed by the Burgess and Council were not only empowered to make the survey, but were expressly “ enjoined and required” to do so. There is a difference between a naked power, which lies at the election of the party to execute or not, .at his pleasure, and an official duty which he is under a legal obligation to perform. In the latter case the preservation of the public rights demands that the whole duty be performed; and where no time is. prescribed within which it is to be completed, the performance of part at one time, is no reason why the residue should not be performed at another. Where a power to graduate the streets was given to the corporation of Georgetown, it was held to be a continuing power to be exercised from time to time: 6 Wheat. 593. In this case, the survey of the southern portion of the borough at one time, is no reason why the northern portion should not be surveyed at another.

The decree of the Quarter Sessions is affirmed.