And be it enacted that at the annual meeting of the trustees of each town for the election of officers, or at any special meeting thereof, for the following purpose, called upon the requisition of any 3 or more of such trustees, of which notice shall be published in 2 successive 'Gazettes,' there shall be chosen by ballot 3 of the said trustees to act as valuators of the property hereinafter mentioned in the said town until the next such annual meeting: Provided that no such valuators shall be chosen at any such meeting, annual or special, unless at least 7 trustees be present thereat.