“ It is claimed that the appellate court erred in holding that the trial court rightly left it to the jury to determine that, if the railway company failed to use the most approved spark arrester, and plaintiff was free from contributory negligence, he could recover. This contention is based upon the assumption that there was no evidence tending to show that the most approved spark arrester was not used. We do not pause to analyze the evidence on the subject, because we think it not necessary to do so. ”

“ Inasmuch as there was evidence to the effect that it is impossible, even with the use of the most effective spark arresters, to prevent the escape of sparks, a case was presented justifying the introduction of expert testimony to aid the jury in determining the ultimate fact whether an engine was in good repair and properly operated which conducted itself as the evidence tended to show this locomotive did. ”