Each issue of such paving bonds shall mature in annual installments of equal or unequal amounts, beginning not more than one year from the date of the bonds and ending not more than two years following the occasion when the last installment of the assessments, in anticipation of whose collection such bonds are issued, shall fall due. In fixing the dates or amounts of annual installments the municipal council shall consider the probable amounts to be collected in each year upon the assessments and shall endeavor, so far as may be practicable, to make the bonds mature in such amounts that the principal of the bonds will be paid by means of the assessments.