The county board of each county in this state is hereby authorized and required to submit to the legal voters thereof, on presentation of a petition of twenty resident freeholders of the county, the proposition to issue bonds, not exceeding twenty thousand dollars, the proceeds of which shall be applied to defray the expenses of boring and prospecting for coal in the county under the direction of the county board thereof; and such board is hereby authorized to issue the bonds for such purposes, in case the vote shall be favorable to the proposition; Provided, however, the county board may, in its discretion, refuse to submit such inquiry to a vote of the people until the next general election after the presentation of such petition.