(a) not likely to be harmful to their health or development; and (b) not such as to prejudice their attendance at school, their participation in vocational orientation or training programmes approved by the competent authority or their capacity to benefit from the instruction received. 2. National laws or regulations may also permit the employment or work of persons who are at least 15 years of age but have not yet completed their compulsory schooling on work which meets the requirements set forth in sub-paragraphs (a) and (b) of paragraph 1 of this Article. 3. The competent authority shall determine the activities in which employment or work may be permitted under paragraphs 1 and 2 of this Article and shall prescribe the number of hours during which and the conditions in which such employment or work may be undertaken. 4. Notwithstanding the provisions of paragraphs 1 and 2 of this Article, a Member which has availed itself of the provisions of paragraph 4 of Article 2 may, for as long as it continues to do so, substitute the ages 12 and 14 for the ages 13 and 15 in paragraph 1 and the age 14 for the age 15 in paragraph 2 of this Article. Article 8 1. After consultation with the organisations of employers and workers concerned, where such exist, the competent authority may, by permits granted in individual cases, allow exceptions to the prohibition of employment or work provided for in Article 2 of this Convention, for such purposes as participation in artistic performances. 2. Permits so granted shall limit the number of hours during which and prescribe the conditions in which employment or work is allowed. Article 9 1. All necessary measures, including the provision of appropriate penalties, shall be taken by the competent authority to ensure the effective enforcement of the provisions of this Convention. 2. National laws or regulations or the competent authority shall define the persons responsible for compliance with the provisions giving effect to the Convention. 3. National laws or regulations or the competent authority shall prescribe the registers or other documents which shall be kept and made available by the employer; such registers or documents shall contain the names and ages or dates of birth, duly certified wherever possible, of persons whom he employs or who work for him and who are less than 18 years of age. Article 10 1. This Convention revises, on the terms set forth in this Article, the Minimum Age (Industry) Convention, 1919, the Minimum Age (Sea) Convention, 1920, the Minimum Age (Agriculture) Convention, 1921, the Minimum Age (Trimmers and Stokers) Convention, 1921, the Minimum Age (Non-Industrial Employment) Convention, 1932, the Minimum Age (Sea) Convention (Revised), 1936, the Minimum Age (Industry) Convention (Revised), 1937, the Minimum Age (Non-Industrial Employment) Convention (Revised), 1937, the Minimum Age (Fishermen) Convention, 1959, and the Minimum Age (Underground Work) Convention, 1965. 2. The coming into force of this Convention shall not close the Minimum Age (Sea) Convention (Revised), 1936, the Minimum Age (Industry) Convention (Revised), 1937, the Minimum Age (Non-Industrial Employment) Convention (Revised), 1937, the Minimum Age (Fishermen) Convention, 1959, or the Minimum Age (Underground Work) Convention, 1965, to further ratification. 3. The Minimum Age (Industry) Convention, 1919, the Minimum Age (Sea) Convention, 1920, the Minimum Age (Agriculture) Convention, 1921, and the Minimum Age (Trimmers and Stokers) Convention, 1921, shall be closed to further ratification when all the parties thereto have consented to such closing by ratification of this Convention or by a declaration communicated to the Director-General of the International Labour Office. 4. When the obligations of this Convention are accepted-(a) by a Member which is a party to the Minimum Age (Industry) Convention (Revised), 1937, and a minimum age of not less than 15 years is specified in pursuance of Article 2 of this Convention, this shall ipso jure involve the immediate denunciation of that Convention, (b) in respect of non-industrial employment as defined in the Minimum Age (Non-Industrial Employment) Convention, 1932, by a Member which is a party to that Convention, this shall ipso jure involve the immediate denunciation of that Convention, (c) in respect of non-industrial employment as defined in the Minimum Age (Non-Industrial Employment) Convention (Revised), 1937, by a Member which is a party to that Convention, and a minimum age of not less than 15 years is specified in pursuance of Article 2 of this Convention, this shall ipso jure involve the immediate denunciation of that Convention, (d) in respect of maritime employment, by a Member which is a party to the Minimum Age (Sea) Convention (Revised), 1936, and a minimum age of not less than 15 years is specified in pursuance of Article 2 of this Convention or the Member specifies that Article 3 of this Convention applies to maritime employment, this shall ipso jure involve the immediate denunciation of that Convention,