CLOPTON, J.

There is no error in refusing to exclude the evidence of Hamner and Bridges, as to the value of the animal killed. The former had been, and was superintendent of plain tiff’s stock farm for several years, and the latter is a farmer engaged in raising and selling cattle, and had raised and sold some half-breed Galloway calves, the animal killed being a thorough-bred Galloway bull. Both of them knew the bull, his breed and peculiar merits. When the witness knows the property, no peculiar skill is requisite to qualify him to testify to its value; neither is it necessary that the opinion of the witness shall be based upon actual sales at the place. Though such sales are more reliable evidence of the market value, the witnesses may give their opinion, based upon general observation and experience, and knowledge of the property and its intrinsic merits.—Ward v. Reynolds, 32 Ala. 384; State v. Finch, 70 Iowa 316; s. c., 59 Am. Rep. 443; Cantlin v. Han. & St. Lo. R. R. Co., 54 Mo. 385; s. c., 14 Am. Rep. 476.

Neither is there error in refusing to exclude the evidence of Hollis and Bridges, which was introduced in rebuttal. The motion to exclude is based upon the grounds, that the witnesses are not shown to be experts, and that the circumstances testified to by them, having occurred at other times than the killing of the animal, and having no connection with it, are irrelevant. While the rule, requiring the evidence to be confined to the issue, excludes all collateral facts not put in issue, by the pleadings, and which are incapable of affording any reasonable inference or presumption as to the principal matter of controversy, it does not exclude any facts which shed light on the main enquiry, and do not terld to withdraw the attention of the jury from such enquiry. In Brickell v. Mills, 128 Mass. 291, in an action for the price of a loom attachment, sold under an agreement that it should work successfully, whether it did so or not, being the question in dispute, the plaintiff, after introducing evidence that the defendant’s loom and another loom were substantially alike in the mechanical arrangements, though different somewhat in details, was permitted to put in evidence that the attachment had worked *284successfully on the latter loom. The evidence was held admissible. And in Gr. Trunk R. R. Co. v. Richardson, 91 U. S. 454, which was an action against a railroad company for injury caused by fire communicated by a locomotive, evidence that at various times during the same summer some of the defendant’s locomotives scattered fire in passing buildings, though it was not shown that either of those which the plaintiff claimed communicated the fire was among the number, or similar in make, was held admissible, as tending to prove a consequent probability that some locomotive caused the fire, and a negligent habit of the officers and agents of the railroad company. These cases are cited as illustrations of the applications of the rule; but we need not extend it so far to sustain the relevancy of the evidence in the present case.

Whether the head-light on defendant’s engine was suitable and effectual, reflecting its light far enough to enable the engineer to discover obstructions on the track in time to stop the train before reaching them, were material enquiries involved in the issue presented by the pleadings.' Any evidence which sheds light on these material enquiries can not be said to be irrelevant. The engineer and fireman having testified, that the head-light would not cast its light so that an obstruction on the track of the size of the animal killed, could be seen in time to avoid injury, it was competent for the. plaintiff to prove, in rebuttal, facts from which the jury might infer that the head-lights in ordinary use on the defendant’s trains reflected light far enough to make obstructions visible at a greater distance, and that the head-light on the particular locomotive was defective, or that the engineer and fireman did not keep a proper lookout. The facts testified to transpired on the same road, and about the part of the road where the animal was killed. The engineer and fireman testified that on the night of the accident there was no fog or moisture, the atmosphere was dry and it was clear. The conditions were the same or less favorable on the occasions testified to by the witnesses. — 7 Amer. & Eng. Ency. of Law, 59, 60.

The court having instructed the jury, if they believed the defendant’s evidence they must find for defendant, there was no error in charging, at the instance of plaintiff, that they “ are not obliged to find for defendant at all events, and if they do not believe the evidence tending to acquit the defendant of negligence, then a verdict may be found for the plaintiff.” It having been shown that the animal was killed by a moving train of defendant, the burden was shifted on the company to show that proper diligence to prevent the injury was used, or *285that, without fault on its part, the animal was not discovered until the peril became so imminent that the injury could not have been averted by use of all the means known to skillful engineers.—Nash. Chatt. & St. Lou. R. R. Co. v. Hembree, 85 Ala. 481. The credibility of the defendant’s witnesses was, and must be, left to the jury; and when the testimony by which the party on whom is cast the burden of proof, attempts to sustain his cause of action or defense, as the case may be, is not believed, the logical result is, an adverse verdict.—Ala. Gr. So. R. R. Co. v. McAlpine, 80 Ala. 73.

The proposition asserted by charge B is, that plaintiff is entitled to recover, if the animal could and ought to have been seen in time for the engineer to check the speed of the train and blow the whistle, though it might not and could not have been seen in time to stop the train, so as to avoid- the injury. When an obstruction on the track could and ought to have been, but was not discovered in time to avert the catastrophe, the actionable negligence consists, not in the omission to check the speed of the ' train, or blow the whistle, but in the failure to keep a proper lookout.—East Tenn., Va. & Ga. R. R. Co. v. Bayliss. 77 Ala. 429. The engineer is not required to check the speed of the train if, when an animal is seen on the track, the injury can not possibly be prevented.

But it is insisted, that any error in the charge is cured by what is designated an explanatory charge given by the court, ex mero motu, to the effectkl that the jury must further believe that the accident could have been prevented if the engineer had seen the bull as soon as he could and ought to have seen him.” Section 2756 of the Code- provides that all charges moved for by either party in writing must be given or refused in the terms in which they are written, and the judge must write thereon given or refused, as the case may be, and sign his name thereto. The section does not prevent giving an explanatory charge, but prohibits the court from qualifying,, limiting or modifying a charge requested and given. A charge asked, which needs qualification or modification to make it a correct legal proposition as applicable to the evidence,' should be refused.—Eiland v. State, 52 Ala. 322. The purpose and office of an explanatory charge is to simplify a charge given,, or to relieve it of involvement or obscurity or to prevent misunderstanding or misapplication. The charge given by the court of its own motion did not explain, but qualified or limited the charge given at request of plaintiff, and does not cure the apparent error.

*286As a general proposition, a railroad company fulfills the duty, and observes the care imposed by the law, when it furnishes its road with such machinery and appliances as are generally used ozi well regulated roads, and have been fouzid sufficient, safe azid prudent. The rule settled by our decisions is, that the companj'- does not owe the duty to adopt new iziventiozrs, though some persons, regarded skillful azrd experienced, may deem them less dazigerous, but that the company fullfils its duty, when it adopts those in ordinazy use by prudently conducted’ and well regulated roads, engaged izi like business, under like circumstazices.—Louis. & Nash. R. R. Co. v. Allen, 78 Ala. 494; Ga. Pac. R'way. Co. v. Propst, 83 Ala. 518; Wilson v. Louis, & Nash. R. R. Co., 85 Ala. 269; Louis. & Nash. R. R. Co. v. Hall, 87 Ala. 708. It is true these were cases of employés; but, izi the case last cited, it is said, generally, “As to appliances — particularly ziew inventions or changes claimed to be improvements — all railroads are not required to coziform to one standard. Allowance is, and must be made, for diversity of opinion, and their use by a majority of roads does not ziecessarily require all railroads to adopt them.” This is the general rule as to the duty and degree of care required of railroad companies.

The rule declared in Memphis & Charleston Railroad Company v. Lyon, 62 Ala. 71, that due care is not observed, when a traizi is ruzi at such speed that it can not be stopped within the limit at which the engineer can plainly see upon a straight track an obstruction thereon of the size of a man or youzig mule, was explaizied and qualified izi Ala. Gt. So. R. R. Co. v. Jones, 71 Ala. 487, as follows: “It was not intended to assert znoi’e than that it is the duty of railroad compaziies to employ the best machinery and appliances which are in use, azid the failure to employ them, in view of the hazardous agencies they control, the dangers necessarily izicidental, is a want of the care and diligence a znan of ordinary prudezice would observe. The omissiozi to provide thezn is a violatiozi of the duty enjoined by law; azid if thei’e is no more in the particular case then the omissiozi azid consequent izijury, the court znay, as a matter of law, declare there is actionable negligezice.” This explaziation was eznphasized in Ala. Gt. So. R. R. Co. v. McAlpine, 75 Ala. 113. Though ziot required to adopt every ziew invention, public policy requires that a railroad company, on account of the hazards incidental to the employment of the powerful agency of steazn, be held to the exercise of the utmost practicable care and diligezice, azid that it keep apace with the improvements of progressive skill and experience, adopting such machinery and appliazices as shall be found by actual *287tests to diminish the perils of life and property incident to the nature of the business. This, as we understand it, is the extent of the meaning of the terms “the best machinery and appliances which are in use,” as employed in the cases referred to above. Utility, demonstrated by use, not the mere fact that an invention is adopted by the best equipped roads, is made the standard of duty. The defect in charge D. consists in this: it makes mere use on the best equipped railroads the test of a proper and good head-light, thus making the acts of such roads, the absolute rule as to the degree of care required of defendant, or other roads, without regard to its actual utility or superiority as demonstrated by the use. Particular machinery and appliances may be in. use on the roads best equipped generally, and yet not the best machinery and appliances in use.

- There is no error in the last charge given at request of plaintiff. Certainly defendant is not excused, if by proper diligence the animal ought to have been seen in time to frighten it off the track, by the mere fact that the engineer did not see it until the train was within sixty feet of the animal.

For the errors mentioned judgment is reversed and cause remanded.