All sewer bonds heretofore attempted to be authorized by any city of the fourth class, under or pursuant to the provisions of sections 3308, 3309 and 3313 of the Compiled Laws of Michigan of 1897, are hereby declared to be when issued legal and binding obligations of said city: Provided, That the proposition to make the loan represented wholly or in part by such bonds received the affirmative votes of 2/3 of the electors voting upon the question at an election actually held in said city, pursuant to 10 days’ notice, notwithstanding any informalities in the ordinance or resolution submitting such proposition to a vote of the electors, and notwithstanding any defects in the publication of said ordinance or resolution, or failure to post copies of such ordinance or resolution as required by said section 3309, or any defects in the notice of the time and place or places of holding such election or of the purpose and object thereof: Provided further, That the amount of the loan represented wholly or in part by said bonds does not exceed the limit imposed by said section 3308.