This is trespass against the mayor of Cambridge and the superintendent of streets, for taking away and removing a building, found incumbering one of the highways of the city. How far it falls within the power of a municipal corporation, with authority to make by-laws for the reasonable regulation of the use of the streets and highways, to authorize their partial incumbrance by the removal of large buildings thereon, with the necessary incidents of occasional detention, and the temporary total obstruction of a highway, it seems to us, it is not necessary to decide in the present case. That it is often useful and convenient that buildings should be so removed is found by experience; it may often be done, with little or no inconvenience to the public, under suitable and proper restrictions, adapted to each particular case; and therefore it seems highly proper that the power to authorize and regulate it should exist somewhere. Perhaps the power vested in municipal corporations to make salutary by-laws, for the regulation of the highways, is sufficient for this purpose. But the right to do what the plaintiff did in the present case, to move a building on the street, so large as effectually to incumber and obstruct it, and, upon an emergency preventing the complete removal in a single day, to leave it on the street for two or more nights, was not claimed as a common law right to the reasonable use of the highways ; but the plaintiff placed his demand, wholly upon the validity of his license, and his compliance with the terms and conditions on which it was granted.
Supposing, therefore, that the act incorporating the city of Cambridge, (St. 1846, c. 109, § 16,) authorizing the city council to make all such salutary and needful by-laws, as towns have power to make, extends to reasonable regulations, in *438regard to the use of the highways, we are to consider how the city council have exercised this power.
By virtue of this provision, the city council passed ordinances, making provision for the appointment of a superintendent of streets, charged, as the designation imports, with the care of the public streets ; and they further passed a bylaw, prohibiting the removal of buildings in the streets, except by a license therefor, to be granted in each particular case by the mayor and aldermen.
The plaintiff relies upon a license granted to him by the mayor to remove the building in question, and insists that the mayor was duly authorized to grant such license by a vote of the mayor and aldermen. The license is produced, and much of the evidence offered at the trial turned upon the question, whether or not the plaintiff had complied with the conditions, on which it was granted.
But the question of law is, whether the mayor alone had authority to grant such license. It appears by the case, that after the passage of the by-law, by the city council, the mayor and aldermen, in May, 1847, passed a vote authorizing the mayor to grant licenses for the removal of buildings, in all cases, in which he might deem it expedient, under the regulations and upon the conditions prescribed by the city ordinance.
The court are of opinion, that the authority thus vested in the board, organized and acting together as an administrative body, could not be delegated by them to a single member, although the constitutional head of such board, to be exercised according to his views of expediency.
By the organization of city governments in this commonwealth, aldermen are elected with a view to their judgment and experience, their knowledge of what is just to the individual, and necessary to public safety and convenience. When, therefore, such a power is granted to the mayor and aldermen, constituted as they are, to act as one deliberative and administrative body, confidence is reposed in then united wisdom and experience, in deciding both upon the fitness of granting a license, dependent on the local position, the *439width of the streets, the magnitude of the building, the season of the year, and all similar circumstances, and in prescribing the. conditions necessary to the public safety and convenience.
And we think this rule is well sustained by authorities. Where by law, two or more justices are authorized to act, they must act together, for this reason, that they should assist each other, and the result of their conference be the ground of their determination. It is deemed not a ministerial act, but a judicial act, in which they are to exercise discretion. The King v. Forrest, 3 T. R. 38; Billings v. Prinn, 2 W. Black. 1017. So where commissioners act upon the propriety of granting a warrant to arrest a witness refusing to come on a summons to be examined. Battye v. Gresley, 8 East, 319.
When such an authority is vested in a committee, or other-body, all must have notice. A majority, unless some other number is made a quorum by the act or law under which they are organized, must meet and act together, when the act of a majority is the act of the body, unless otherwise determined by then- constitution. Commonwealth, v. Ipswich, 2 Pick. 70; Damon v. Granby, 2 Pick. 345; Williams v. Lunenburg, 21 Pick. 75.
But it is contended for the plaintiff, that the defendant Green is estopped from setting up the invalidity of a license granted by himself. But the court are of opinion, that the plaintiff cannot avail himself of such an estoppel in pais.
An estoppel is to be construed strictly, and if it could avail at all, as against the mayor, it could not apply to Coolidge, who was a public officer, charged with a public duty, to remove all nuisances in the highways. But a more satisfactory, and we think a legal reason extending as well to Green, the mayor, as to the superintendent of streets, is, that the mayor acting in a public capacity, in the exercise of a public duty, and as trustee for the public, could not estop himself from so acting, by his previous personal and unauthorized act. Fairtitle v. Gilbert, 2 T. R. 169.
On these grounds, the court are of opinion, that the defendants were not estopped from denying the validity of the *440license under which the plaintiff acted. The jury having, foi the purposes of the trial, been directed otherwise on these points of law, the verdict must be set aside, and a new trial granted.