This operation of sympathy is strikingly illustrated in the penal codes of primitive communities, both by the mildness of the punishments inflicted for homicide, and by the startling differences between the penalties allotted to the same crime according as the criminal was taken in the act or not. ``It is curious to observe'', says Sir H. Maine (Ancient Law, chap. x.), ``how completely the men of primitive times were persuaded that the impulses of the injured person were the proper measure of the vengeance he was entitled to exact, and how literally they imitated the probable rise and fall of his passions in fixing the scale of punishment.'' And even in more civilised societies there is a very common feeling of uncertainty as to the propriety of inflicting punishment for crimes committed long ago, which seems traceable to the same source.