Section 1. Be it enacted, &c., That when, in the opinion of the county commissioners of any county, the cost of building a county bridge or bridges to be erected therein, or the said county's proportionate share of the cost of a bridge to be erected over a river or stream upon the line between it and an adjoining county, or the cost of acquiring a toll bridge or bridges in any county or a toll bridge erected over a river or stream upon the line between adjoining counties, is so large in amount that to provide the funds necessary to pay the same by a single tax levy would be burdensome to the taxpayers, said commissioners, having first secured the approval of the court of quarter sessions of their county so to do, may issue and sell to the highest bidder, at not less than their face value, interest bearing bonds of the county for the purpose of raising funds to defray the costs aforesaid.