Take again the law of ancient lights in England. An obstruction to be actionable must be substantial. Under ordinary circumstances the erection of a structure a hundred yards off, and one foot above the ground, would not be actionable. One within a foot of the window, and covering it, would be, without any finding of a jury beyond these facts. In doubtful cases midway, the question whether the interference was substantial has been left to the jury. /4/ But as the elements are few and permanent, an inclination has been shown to lay down a definite rule, that, in ordinary cases, the building complained of must not be higher than the distance of its base from the dominant windows. And although this attempt to work out an exact line requires much caution, it is entirely philosophical in spirit. /5/ The same principle applies to negligence. If the whole evidence in the case was that a party, in full command of [129] senses and intellect, stood on a railway track, looking at an approaching engine until it ran him down, no judge would leave it to the jury to say whether the conduct was prudent. If the whole evidence was that he attempted to cross a level track, which was visible for half a mile each way, and on which no engine was in sight, no court would allow a jury to find negligence. Between these extremes are cases which would go to the jury. But it is obvious that the limit of safety in such cases, supposing no further elements present, could be determined to a foot by mathematical calculation. The trouble with many cases of negligence is, that they are of a kind not frequently recurring, so as to enable any given judge to profit by long experience with juries to lay down rules, and that the elements are so complex that courts are glad to leave the whole matter in a lump for the jury's determination. I reserve the relation between negligent and other torts for the next Lecture. LECTURE IV. -- FRAUD, MALICE, AND INTENT.--THE THEORY OF TORTS. [130] The next subjects to be considered are fraud, malice, and intent. In the discussion of unintentional wrongs, the greatest difficulty to be overcome was found to be the doctrine that a man acts always at his peril. In what follows, on the other hand, the difficulty will be to prove that actual wickedness of the kind described by the several words just mentioned is not an element in the civil wrongs to which those words are applied.