Sometimes courts are induced to lay down rules by facts of a more specific nature; as that the legislature passed a certain statute, and that the case at bar is within [151] the fair meaning of its words; or that the practice of a specially interested class, or of the public at large, has generated a rule of conduct outside the law which it is desirable that the courts should recognize and enforce. These are matters of fact, and have sometimes been pleaded as such. But as their only importance is, that, if believed, they will induce the judges to lay down a rule of conduct, or in other words a rule of law, suggested by them, their tendency in most instances is to disappear as fast as the rules suggested by them become settled. /1/ While the facts are uncertain, as they are still only motives for decision upon the law,--grounds for legislation, so to speak,--the judges may ascertain them in any way which satisfies their conscience. Thus, courts recognize the statutes of the jurisdiction judicially, although the laws of other jurisdictions, with doubtful wisdom, are left to the jury. /2/ They may take judicial cognizance of a custom of merchants. /3/ In former days, at least, they might inquire about it in pais after a demurrer. /4/ They may act on the statement of a special jury, as in the time of Lord Mansfield and his successors, or upon the finding of a common jury based on the testimony of witnesses, as is the practice to-day in this country. But many instances will be found the text-books which show that, when the facts are ascertained, they soon cease to be referred to, and give place to a rule of law. [152] The same transition is noticeable with regard to the teachings of experience. There are many cases, no doubt, in which the court would lean for aid upon a jury; but there are also many in which the teaching has been formulated in specific rules. These rules will be found to vary considerably with regard to the number of concomitant circumstances necessary to throw the peril of conduct otherwise indifferent on the actor. As the circumstances become more numerous and complex, the tendency to cut the knot with the jury becomes greater. It will be useful to follow a line of cases up from the simple to the more complicated, by way of illustration. The difficulty of distinguishing rules based on other grounds of policy from those which have been worked out in the field of negligence, will be particularly noticed.