[1] In his first assignment of error defendant contends that in the following instance he was denied the right to confront the witnéss, Lenny Harrelson:
“Q. Of course, you realize if you had anything to do :with starting the argument with him that your family might hold you responsible for your sister’s death, don’t you?
Me. Moore: Objection.
Court : Sustained.”
Latitude of cross-examination is a matter well within the discretion of the trial court. State v. McPherson, 276 N.C. 482, 172 S.E. 2d 50; State v. Dickens, 11 N.C. App. 892, 181 S.E. 2d 257. Although defendant is entitled to elicit facts which tend *220to show bias in order to impeach a witness, see 1 Stansbury, N.C. Evidence (Brandis rev.), § 45, he has failed to show how he may have been prejudiced by the trial court’s refusal to allow this witness to respond to a clearly argumentative question. The jury knew the witness was decedent’s brother and that he was present at the time of the shooting.
[2] Defendant next assigns as error the trial court’s determination that the three minor witnesses were competent to testify. Competency of witnesses is clearly within the trial court’s discretion and is reviewable only in case of abuse, which does not here appear. 7 Strong, N. C. Index 2d, Witnesses, § 3, p. 693; McCurdy v. Ashley, 259 N.C. 619, 131 S.E. 2d 321. The test of competency is the capacity to understand and relate under oath facts which will assist the jury in finding the ultimate facts. State v. Cooke, 278 N.C. 288, 179 S.E. 2d 365. Each of the children stated on voir dire that he knew what it meant to swear to tell the truth. From his observation of their intelligence and demeanor, the trial court had ample grounds from which to conclude that each child was a competent witness.
[3] Defendant’s third assignment of error concerns the admissibility of polygraph evidence. In State v. Foye, 254 N.C. 704, 708, 120 S.E. 2d 169, 172, our North Carolina Supreme Court rejected such evidence, saying:
“[W]e are of opinion that the foregoing enumerated difficulties alone [lack of general scientific recognition, tendency to distract the jury, inability to cross-examine machine, no corresponding necessity for submission to tests by the prosecution] in conjunction with the lie detector use presents obstacles to its acceptability as an instrument of evidence in the trial of criminal cases, notwithstanding its recognized utility in the field of discovery and investigation, for uncovering clues and obtaining confessions. This conclusion is in line with the weight of authority repudiating the lie detector as an instrument of evidence in the trial of criminal cases.”
Defendant nevertheless urges us to accept the polygraph in light of technological and judicial advances since Foye was decided in 1961. The weight of authority still supports the Foye view, however, see Annot., 23 A.L.R. 2d 1306 (Later Case Service 1970), and we decline to hold adherence to Foye to be prejudicial error.
*221Assignments of error four and five deal with evidence which was properly excluded as irrelevant or hearsay and merit no further discussion.
[4] Defendant’s last assignments of error involve the court’s charge to the jury. Citing State v. Bright, 237 N.C. 475, 478, 75 S.E. 2d 407, 409, he contends that the court erred in failing to charge that a reasonable doubt must be “one growing out of the evidence or the insufficiency of the evidence.” We do not agree with this contention. When the evidence is direct and not circumstantial and there is ample evidence to support the verdict, an unqualified instruction on reasonable doubt is not prejudicial. State v. Gaiten, 277 N.C. 236, 176 S.E. 2d 778; State v. Britt, 270 N.C. 416, 154 S.E. 2d 519.
[5] Defendant next urges this Court to overrule its decision in State v. Williams, 6 N.C. App. 611, 170 S.E. 2d 640, holding that it was not error to fail to give an instruction to scrutinize interested prosecution witnesses as well as interested defense witnesses. In Williams, we concluded that to require such instruction would “ ‘improperly and prejudicially’ discredit the testimony of the prosecuting witnesses and would be an unwarranted extension of the interested witness rule. ...” Id. at 613, 170 S.E. 2d at 641. We continue to follow this rationale and find no error in the instruction given.
[6] Defendant also contends that the court erroneously instructed on the elements of involuntary manslaughter by failing properly to define proximate cause and unlawful pointing of a gun. After reviewing the charge we feel that the court correctly defined the crime of involuntary manslaughter and properly outlined the elements necessary for the State to prove in order to find defendant guilty of involuntary manslaughter. Defendant argues that under State v. Mizelle, 13 N.C. App. 206, 185 S.E. 2d 317, the trial court is required to instruct that foreseeability is an element of proximate cause. In that opinion this Court cited State v. Dewitt, 252 N.C. 457, 114 S.E. 2d 100, wherein the North Carolina Supreme Court held that the trial court must instruct fully on proximate cause as it relates to the facts of the particular case. In Mizelle, defendant was indicted and convicted on a charge of involuntary manslaughter. In the case at bar, defendant was indicted on a charge of first degree murder and was convicted of second degree murder. Under the facts of the case, foreseeability was not seriously in issue. Defendant admitted that he held a loaded gun and pointed it at *222Lenny Harrelson, who was standing close to decedent. We find the instruction sufficient on both causation and the unlawful act. State v. DeWitt, supra. Accord, State v. Phelps, 242 N.C. 540, 89 S.E. 2d 132; State v. Sawyer, 11 N.C. App. 81, 180 S.E. 2d 387. For the reasons stated above, we also find no error in the proximate cause portion of the instruction on second degree murder.
[7] Defendant contends that in instructing the jury “[i]n determining whether the thirty-eight caliber pistol is a deadly weapon,” the court expressed an opinion that defendant’s .38 caliber gun caused his wife’s death. This contention is without merit. Defendant stipulated that his wife died as the result of a gunshot wound and testified that he had his .38 caliber gun in his hand when his wife entered the room and the gun fired. The court was not expressing an opinion but merely reciting-evidence not in dispute.
[8] In defining heat of passion, the trial court said:
“It means that the defendant’s state of mind was at the time so violent as to overcome his reason, so much so that he could not think to the extent necessary to form a deliberate purpose and control his actions.”
Defendant argues that such instruction requires him to be legally insane in order to negate the element of malice and to reduce the offense from murder to manslaughter. See State v. Wynn, 278 N.C. 513, 180 S.E. 2d 135; State v. Cooper, 273 N.C. 51, 159 S.E. 2d 305. We disagree. In State v. Jennings, 276 N.C. 157, 161, 171 S.E. 2d 447, 450, the North Carolina Supreme Court quoted with approval Black’s Law Dictionary’s definition of heat of passion as “rage, anger, hatred, furious resentment, or terror, rendering the mind incapable of cool reflection.” Legal insanity, in contrast, requires that the accused be laboring under such defect of reason from disease of the mind as to be incapable of knowing the nature and quality of his act, or if he does know this, not to know right from wrong. State v. Mercer, 275 N.C. 108, 165 S.E. 2d 328. The trial court’s definition of heat of passion fell far short of the insanity test approved by our courts and placed no improper burden on defendant.
We have examined defendant’s other assignments of error relating to the charge and find all to be without merit. While isolated portions of the charge may be somewhat incomplete, they will be read in context. State v. Bailey, 280 N.C. 264, 185 *223S.E: 2d 683, cert. denied, 409 U.S. 948 (1972). In this light they appear to charge adequately on the material aspects of the case arising on the evidence. See State v. Craddock, 272 N.C. 160, 158 S.E. 2d 25.
Defendant has been accorded a vigorous defense, but the evidence against him was strong and convincing. While he may not have received a perfect trial, he has received a trial free from prejudicial error.
No error.
Chief Judge Brock and Judge MORRIS concur.