4. A person to whom this Order applies who establishes to the satisfaction of the Revenue Commissioners that he has borne or paid tax at a rate in excess of the rate per cent for the time being specified in section 11 (1) (a) of the Act in relation to the supply to or importation by him of any instrument or appliance of a kind commonly used to make a diagnosis, to prevent or treat an illness, to carry out a surgical operation or to carry out scientific research and who fulfils to the satisfaction of the Revenue Commissioners the conditions which are specified in paragraph 5 of this Order shall be entitled to be repaid so much of such tax as is specified in paragraph 6 of this Order.