Where the prosecution relies exclusively upon circumstantial evidence for a conviction, it is the duty of the trial judge, whether so requested or not, to instruct the jury on the rule of law applicable to such evidence, as laid down in section 984 of the Penal Code. Riley v. State, 1 Ga. App. 651 (57 S. E. 1031); McElroy v. State, 125 Ga. 37 (53 S. E. 759). Judgment reversed.