The plaintiff assigns as error, based on his exceptions Nos. 37 and 38, the trial court’s sustaining the defendant’s objections to two questions asked Dr. John Chamblee. Dr. Chamhlee is health officer of Nash County; a doctor of medicine, licensed to practice his profession, *148wbo bad studied chemistry two years at college. Dr. Chamblee was offered by the plaintiff as a layman, who had studied chemistry, and not as an expert; and as a man who was familiar with the type of cargo tank truck such as exploded in the instant case. Dr. Chamblee was asked this hypothetical question in substance: assuming that the jury should find that the tank truck was unloaded of its gasoline around noon on Saturday, the tank drained, all the known openings closed and fastened; that it was taken to Rocky Mount, was washed and greased, and thereafter driven to the Hopkins’ yard where it remained about 30 hours; that it was not exposed to any outside fire producing agency, and around 5 :15 p. m. on the next day violently exploded, did he have an opinion satisfactory to himself as to what caused the explosion? The court sustained defendant’s objection to the question, which is the basis of plaintiff’s exception No. 37. Dr. Chamblee, if permitted to answer, would have replied: in his opinion the explosion would be caused from spontaneous combustion on the inside of the tank. Dr. Chamblee was then asked, considering his familiarity with this type tank, if he had an opinion as to what would cause an explosion of an empty tank recently emptied of gasoline, eliminating any external causes. If permitted to answer, over defendant’s objection, he would have given the same answer he did to the hypothetical question. This is plaintiff’s exception No. 38.
’ In both of these questions Dr. Chamblee was asked to give his opinion upon facts not within his personal knowledge — in other words to give expert testimony. These questions present this question: was Dr. Cham-blee better qualified than the jury to form an opinion from these facts? This Court has said in Patrick v. Treadwell, 222 N.C. 1, 21 S.E. 2d 818: “it would seem that the proper test is whether additional light can be thrown on the question under investigation by a person of superior learning, knowledge or skill in the particular subject, one whose opinion as to the inferences to be drawn from the facts observed or assumed is deemed of assistance to the jury under the circumstances.” (Italics ours).
A witness to be competent as an expert must be shown to be skilled or experienced in the business, profession or science to which the subject relates, though there is no exact requirement as to the mode by which such knowledge, skill or experience has been acquired. S. v. Smith, 221 N.C. 278, 20 S.E. 2d 313; 20 Am. Jur., Evidence, Sec. 784; Stansbury N. C. Evidence, Sec. 133; Wigmore on Evidence, Third Ed., Sec. 1923.
Dr. Chamblee by education, training and experience is well qualified as a physician to give an opinion which would be likely to aid a jury to a correct conclusion as to the diseases and ills constantly threatening and affecting humanity. However, it does not appear that Dr. Chamblee is qualified by education, training or experience to express an opinion as an *149expert witness as to the cause of the explosion in this case. The rulings of the trial court as to this assignment of error were correct.
The plaintiff assigns as error the refusal of the trial court, over defendant’s objection, to hold that Herman Baker had qualified as an expert witness for plaintiff, and the refusal of the trial court to permit him, over defendant’s objection, to say where he kept his cargo tank trucks, how he loaded and unloaded them, and to express an opinion upon assumed facts. This assignment of error is based on his exceptions Nos. 39-43, both inclusive. Herman Baker has been an oil distributor 32 years, and is familiar with the equipment he uses. The record is bare of any evidence that Herman Baker by his business, knowledge, trade or experience is qualified to give an opinion as an expert witness as to the explosion in this case. The plaintiff contends Herman Baker’s evidence was excluded under an erroneous view of the law, citing Pridgen v. Gibson, 194 N.C. 289, 139 S.E. 443. It is a far cry from the facts in that case and in this. In the Pridgen Case it was held error for the trial court to hold as a matter of law that a general practitioner of medicine could not qualify as an expert to give his opinion in a personal injury case for alleged malpractice, though he had not specialized as an oculist. This exceptive assignment of error is overruled.
This brings us to a consideration of plaintiff’s assignment of error as to the trial court allowing defendant’s motions for judgments of nonsuit in all three cases, made at the close of all the evidence. We do not consider the defendant’s evidence on such a motion, unless favorable to the plaintiff, except when not in conflict with plaintiff’s evidence, it may be used to explain, or make clear the evidence of the plaintiff. Harrison v. R. R., 194 N.C. 656, 140 S.E. 598; Rice v. Lumberton, 235 N.C. 227, 69 S.E. 2d 543; Polansky v. Ins. Asso., 238 N.C. 427, 78 S.E. 2d 213.
“Everybody knows that a lighted match will ignite kerosene or fuel oil.” Jennings v. Oil Co., 206 N.C. 261, 173 S.E. 582. If is common knowledge that gasoline is highly inflammable. American Oil Co. v. Nicholas, 156 Va. 1, 157 S.E. 754. “It is a matter of general knowledge that gasoline is highly volatile, and gives off fumes and vapors which readily ignite when in the proximity of a flame.” Bradley v. Fowler, 210 S.C. 231, 42 S.E. 2d 234. Webster’s New Collegiate Dictionary (1949) gives as one definition of the word cap: “a percussion cap; also a small piece of paper containing an explosive charge, used in toy pistols.” It is common knowledge that the firing of a cap pistol, or the explosion of a cap by such pistol, emits a spark, and that a spark will ignite gasoline or gasoline fumes or vapors.
Judicial notice is not limited by the actual knowledge of any individual judge or court. Judges may inform themselves, or refresh their memo*150ries, from standard works of reference, though it is settled law that the mere appearance of facts therein does not entitle them to judicial notice, unless they are such as to be part of common knowledge. 20 Am. Jur., Evidence, sections 21 and 22; Siemen's Estate, 346 Pa. 610, 31 A. 2d 280, 153 A.L.R. 483, writ of certiorari denied in 320 U.S. 758, 88 L. Ed. 452.
The plaintiff contends in his brief : (a) there was no positive and direct evidence which indicated any definite explanation for the explosion, save what could be inferred from the evidence that the defendant was negligent, and failed to exercise due care in the operation and maintenance of the tank truck; (b) that the front and back ends of the tank truck were ripped out, but the dome cap was not dislodged, but was closed and securely fastened, and the evidence discloses that safety devices in the dome cap were defective in that the fusible plugs did not melt or blow out as it was intended they should to prevent explosion; (c) it is common knowledge that tank trucks do not ordinarily explode when properly inspected, supervised and operated, whether loaded or not, that this tank truck was in the sole control of defendant, “and, therefore, the evidence in this case discloses a typical background for the doctrine of res ipsa loquitur”: the plaintiff cites in his brief Howard v. Texas Co., 205 N.C. 20, 169 S.E. 832.
The plaintiff’s uncontradicted evidence shows that the Hopkins boys, who were killed, and Harold Whitley shortly before the explosion were playing in the yard where the tank truck was, though not near it, when Oliver Hopkins went in his house. He was in the house at the time of the explosion. Don Hopkins and Harold Whitley had cap pistols before the explosion; after the explosion cap pistols, or some parts of them, were found out across the field; that afternoon his wife went to an airport just across the road, and found a cap pistol.
Without considering defendant’s evidence that the Coroner of Nash County found a cap that had been fired from a cap pistol or some other instrument within 5 feet of the tank; that a roll of caps was in the pocket of the dead body of Duane Hopkins, it is our opinion that the evidence offered by plaintiff is not sufficient, when most liberally construed, and giving to him the benefit of every reasonable inference to be drawn therefrom, to carry the cases to the jury that the explosion was caused by any negligence of the defendant in the operation and maintenance of the tank truck, or that the safety devices on the tank truck were defective, and that the allowing of the motions for judgments of nonsuit in each case was proper, unless the doctrine of res ipsa loquitur applies. It is to be noted that plaintiff states in his brief there was no direct and positive proof which indicated any explanation for the explosion, except such as could be inferred from the evidence. There is an utter want of direct *151proof tbat any safety devices on tbe tank truck were defective. Cases cannot be submitted to a jury on speculations, g-uesses or conjectures. Negligence is not presumed from tbe mere fact someone is killed. Mills v. Moore, 219 N.C. 25, 12 S.E. 2d 661.
Upon all tbe facts disclosed by tbe evidence “more than one inference can be drawn from tbe evidence as to tbe cause” of tbe explosion, and “tbe existence of negligent default is not tbe more reasonable probability, and tbe proof of tbe occurrence, without more, leaves tbe matter resting only in conjecture.” Therefore tbe doctrine of res ipsa loquitur does not apply, because tbe cases fall within the exceptions pointed out in Springs v. Doll, 197 N.C. 240, 148 S.E. 251; Jennings v. Oil Co., supra; Boone v. Matheny, 224 N.C. 250, p. 253, 29 S.E. 2d 687 (see also Lamb v. Boyles, 192 N.C. 542, 135 S.E. 464; Dail v. Taylor, 151 N.C. 284, 66 S.E. 135): rather than within the typical explosion eases, such as Howard v. Texas Co., supra.
Considering plaintiff’s evidence, and defendant’s evidence, which is not in conflict with it, but tends to explain and make clear plaintiff’s evidence, it would seem tbat tbe tank truck was not under tbe exclusive control of tbe defendant, and tbe doctrine of res ipsa loquitur is not applicable, because the cases fall within another exception to tbe rule as set forth in Springs v. Doll, supra; see Saunders v. R. R., 185 N.C. 289, 117 S.E. 4; Smith v. Oil Co., 239 N.C. 360, 79 S.E. 2d 880. This would seem to be true, without considering at all defendant’s evidence tending to show tbat two children were on top of tbe tank of the truck, and tbe larger boy bad tbe dome lid on tbe tank truck open, and was kneeling down at it.
Tbe remaining assignment of error discussed in plaintiff’s brief relates to the exclusion of evidence as to funeral expenses. From what we have said above tbe exclusion of this evidence was harmless.
Tbe untimely deaths of these four, fine young boys present a case of stark, heart breaking tragedy. We have tbe utmost sympathy for tbe bereaved parents, but it is our duty “to keep tbe law in calmness made.”
Tbe judgments entered in tbe Superior Court are