Summary assessment powers allow immediate tax assessment to protect revenue; person in charge deemed taxable when taxpayer unascertainable. Proper officers, with prior approval of an Additional or Joint Commissioner, may make summary assessments where evidence of tax liability emerges and delay would harm revenue; if the taxable person is unascertainable for goods, the person in charge is deemed taxable. The Commissioner may withdraw erroneous summary orders and refer the case back to ordinary reassessment procedures.