( 1 ) THE facts of this case are shortly as follows:

( 2 ) THE petitioner is the Burma Shell Oil Storage and Distributing Company of India Limited, a well-known company which produces manufactures, distributes and sells mineral oil, petroleum, etc. including aviation spirit. It carries on business inter alia in Calcutta in the distribution and sale of oil. It has a supply station at Dum-Dum Aerodrome, from which motor spirit for aviation purposes called "aviation spirit" is supplied to aircraft, including foreign-bound aircraft. As is to be expected, most of the aircraft so supplied, proceed beyond Indian territorial limits. The Bengal Motor Spirit Sales Taxation Act, being Bengal Act V of 1951, provides for the levy of a tax on retail sales of motor spirit in Bengal. Under Section 2 of the said Act, "motor Spirit" has been defined to be any liquid or admixture of liquids which is ordinarily used directly or indirectly as fuel for any form of motor vehicle or stationary internal combustion engine, having a flash-point below 76 degrees Farenheit. Under Section 4 (4), sale of motor spirit for the purpose of aviation had been excluded. By virtue of an amendment introduced b