Section 3. The board shall hold public hearings annually on the first Thursday in May and November, and at such other times as it may determine, on petitions for changes in the rules formulated by it. If, after any such hearing, it shall deem it advisable to make changes in said rules, it shall appoint a day for a further hearing, and shall give notice thereof and of the changes proposed by advertising in at least one newspaper in each of the cities of Boston, Worcester, Springfield, Fall River, Lowell and Lynn, at least ten days before said hearing. If the board on its own initiative contemplates changes in said rules, like notice and a hearing shall be given and held before the adoption thereof.