(3) In cases in which the evidence is not taken down in writing by the Magistrate or Session Judge, he shall, as the examination of each witness proceeds, make a memorandum of the substance of what such witness deposes; and such memorandum shall be written and signed by the Magistrate or Sessions Judge with his own hand, and shall form part of the record. (4) If the Magistrate or Sessions Judge is prevented from making a memorandum as above required, he shall record the reason of his inability to make it.