And be it enacted, that any summons or notice, or any writ or other proceeding at law or in equity, requiring to be served upon the promoters of the undertaking, may be served by the same being left at or transmitted through the post directed to the principal office of the promoters of the undertaking, or one of the principal officers where there shall be more than one, or being given or transmitted through the post directed to the secretary, or in case there be no secretary the solicitor of the said promoters.