Sections 18A, 42 and 43 of the Act, as they stood at the material time, are to the following effect: "18A. (1)(a) In the case of income in respect of which provision is not made under section 18 for deduction of income tax at the time of payment, the Income tax officer may, on or after the 1st day of April in any financial year, by order in writing, require an assessee to pay quarterly to the credit of the Central Government on the 15th day of June, 15th day of September, 15th day of December and 15th day of March in that year, respectively, an amount equal to one quarter of the income tax and super tax payable on so much of such income as is included in his total income of the latest previous year in respect of which he has been assessed, if that total income exceeded the maximum amount not chargeable to tax in his case by two thousand five hundred rupees.