All taxes shall
be uniform upon the same class of subjects within the territorial limits, of the
authority levying the tax, and shall be levied and collected under general laws,
which shall prescribe such regulations as shall secure a just valuation for taxation of
all property, real and personal: provided, that the legislature may allow such
exemptions from taxation from time to time as shall seem necessary and just, and all
existing exemptions provided by the laws of the territory, shall continue until
changed by the legislature of the state: provided further, that duplicate taxation of
property for the same purpose during the same year, is hereby prohibited.