erally be based upon culpability. But in some quarters, entitled to respect, there is still a tendency to hold that, when real estate is damaged or invaded, the old rule of absolute liability remains unchanged.14 On principle, and on the weight of modern authority, there is (in the absence of culpability) no liability for accidental damage or entry in the case of real estate any more than in the case of damage done to personalty or to the person.' 15 If fault is requisite to an action for defendant's personal entry upon plaintiff's land, there can be no reason why it should not be requisite to an action for damage to plaintiff's land, due to acts done by defendant upon defendant's land without personal entry by defendant upon plaintiff's land. Suppose that acts are done by defendant upon defendant's land, which have the effect of causing deleterious things to pass from defendant's land upon or over plaintiff's land, thereby damaging plaintiff's land or impairing plaintiff's comfortable enjoyment of his land. Such a case is generally classed under the head of nuisance, as distinguished from trespass. Mr. Salmond speaks of it as a nuisance "in the strict sense of that term." 16 Is it requisite to defendant's liability that his acts done upon his own land should be blameworthy? We should say yes, as a general rule, subject, however, to an exception in those cases where defendant's acts fall within the so-called "extra-hazardous class." As to the requirement of fault, there is a conflict of authority. But if we are right in the position that plaintiff must prove fault in an action for personal entry, it is difficult to see how the plaintiff can claim to occupy more favorable ground in the present supposed Defendant is liable if, without justification,17 he inten case. 4 See MARKBY, ELEMENTS OF LAW, 3 ed., § 711; and compare 3 HOLDSWORTH, HISTORY OF ENGLISH LAW, 306. 15 See Professor Whittier, as to real estate, 15 HARV. L. REV. 347; and compare as to personalty, 342; and as to the person, 339. See also, as to real estate: Losee v. Buchanan, 51 N. Y. 476 (1873), and see Earl, C., p. 490; Brown v. Collins, 53 N. H. 442 (1873); Marshall v. Welwood, 38 N. J. L. 339 (1876); all opposing the reasoning in the House of Lords in the then recent decision in Rylands v. Fletcher, L. R. 3 H. L. 330 (1868). See, also, Opinion of Martin, B., in Fletcher v. Rylands, 3 Hurl. & Colt. 774, 793 (1865); and argument of Mr. Mellish in that case, p. 785. See further, Laws OF ENGLAND, edited by Lord Halsbury, vol. 27, § 1515; Rumbold v. London County Council, 25 T. L. R. 541 (1909); Salmond, Torts, 1 ed., 159. 16 SALMOND, TORTS, 4 ed., 175. 17 The justification most frequently set up is that defendant's acts do not exceed his right to make a reasonable use of his own land. tionally or negligently inflicts substantial damage upon the plaintiff.18 Would the adoption of the requirement of fault in this class of cases prevent recovery in a large proportion of litigated suits where plaintiff could have prevailed if the rule of absolute liability was adopted? We think not; and for two reasons: 1. Fault, as heretofore defined, exists, and is easily provable, in a great majority of cases where damage has resulted. And this is so even where the damage sued for occurred as a first result of the dangerous condition. 2. In a majority of litigated cases the damage sued for was continuous, or at least occurred repeatedly.19 Assuming that the defendant was not at fault for not foreseeing the first outbreak or harm, and hence was absolved from liability for damage occurring in the first instance, still, after he knows that damage has occurred and is likely to repeatedly occur, he is liable for failing to obviate the cause of the subsequently occurring damage. “If he fails to do so, his liability from such time must, upon principle, be the same as it would have been could he have foreseen the result in the first instance." His liability arises "from a continuance of the cause of injury, after its character becomes apparent." 20 Thus, if the defendant knew the damaging effect of a spout maintained by him, he would be answerable for the harm it subsequently did "until he stopped it." 21 18 As to what constitutes sufficient damage, see SALMOND, TORTS, 4 ed., 214-17. 19 An author who thinks that an isolated escape of a deleterious thing on to plaintiff's land might be classed under nuisance, says: "Nuisance is commonly a continuing wrong; that is to say, it commonly consists in the establishment or maintenance of some state of things which continuously or repeatedly causes the escape of noxious things on to the plaintiff's land." SALMOND, TORTS, 4 ed., 211. 20 Crawford v. Rambo, 44 Ohio St. 279; 286-87, 7 N. E. 429 (1886); Davis v. Rich, 180 Mass. 235, 62 N. E. 375 (1902), Holmes, C. J., p. 238; GLEGG, REPARATION, I ed., 282. 21 See Davis v. Rich, 180 Mass. 235, 238, 62 N. E. 375 (1902). The conflict of authority as to the requirement of fault is not confined to the particular kind of nuisance above discussed, but exists as to certain other varieties of nuisance. In the books the broad question is sometimes raised, whether the requirement of fault exists as to the general subject of nuisance. See Judge Cooley in favor of the general requirement of fault; TORTS, 2 ed., 670-71. For apparently opposing views, see 29 CYCLOPEDIA LAW AND PROCEDURE, 1155; I WOOD, NUISANCE, 3 ed., 48; 2 WOOD, 783; 21 Laws of ENGLAND (Halsbury), § 845, p. 507. But an attempt The third class (absolute liability where there is neither breach of contract nor fault) is largely made up of two elements which have often been spoken of as if they were entirely distinct from each other. Division 1. Cases of absolute liability which, heretofore, have usually been classed under tort. Division 2. Cases of absolute liability which, heretofore, have been regarded as more nearly akin to breach of contract than to tort. In both divisions there is an obligation imposed by law, in the absence of either contract or fault on the part of defendant.22 Consider now: Cases of absolute liability in absence of fault, which heretofore have usually been classed under tort. (Division 1, supra.) These cases may be divided into three classes: (a) Liability for non-culpable mistake. (b) Liability for non-culpable accident. (c) Vicarious liability for the wrongful acts of others.23 The last class (c) is generally dealt with under the law of master to answer this question as to the general subject would involve hopeless confusion, on account of the ambiguity, the vagueness, and the broadness of the term nuisance. A "wide range of subject-matter" is embraced under it. The term nuisance, when used as denoting an actionable tort, is not confined to denoting a single specific kind of tort. It is "a term of classification applied to a group into which certain wrongs are gathered for convenience of reference." TERRY, LEADING PRINCIPLES OF ANGLO-AMERICAN LAW, § 434. It is used as including under one general head various subjects which, upon any scientific principles of classification, do not belong together, and most or all of which are to be found under various separate and distinct titles of the law. The wrongs classed under the general head of nuisance "are breaches of various duties." See INNES, TORTS, Preface, 4; BISHOP, NON-CONTRACT Law, § 411, n. 1; SALMOND, TORTS, 4 ed., 210; Prof. E. R. Thayer, 27 HARV. L. Rev. 326. Legal authors admit the difficulty, not to say the impossibility, of framing a general definition of the term nuisance. Judge Cooley says: "It is very seldom, indeed, that even a definition of a nuisance has been attempted, for the reason that, to make it sufficiently comprehensive, it is necessary to make it so general it is likely to define nothing." TORTS, 2 ed., 672. Mr. Garrett says: "It is indeed impossible, having regard to the wide range of subject-matter embraced under the term nuisance, to frame any general definition. . . ." GARRETT, NUISANCE, 3 ed., 4. Instead of discussing the broad question, whether the requirement of fault exists as to the general subject of nuisance, it would be better to consider separately what the rule as to fault is in regard to each of the various incongruous topics which are usually lumped together under the one general head of nuisance. " KEENER, QUASI-CONTRACTS, 15; ANSON, CONTRACTS, 12 ed., 8. and servant and the law of domestic relations. It will not be discussed here. To consider the two first classes (a and b) we must begin by distinguishing between accident and mistake. "A case of accident then is one where the effect was neither intended nor was so probable a result as to make the conduct negligent. On the contrary, in the cases of mistake that arise the effect is intended, and the error consists in thinking that such an effect is not tortious." 24 "The plea of inevitable accident is that the consequences complained of as a wrong were not intended by the defendant and could not have been foreseen and avoided by the exercise of reasonable care. The plea of inevitable mistake, on the other hand, is that, although the act and its consequences were intended, the defendant acted under an erroneous belief, formed on reasonable grounds, that some circumstance existed which justified him." 25 "Accident, in this System, means an event happening without the concurrence of the will of the person by whose agency it was caused. It differs from mistake, because the latter always supposes the operation of the human will in producing the event, although that will is caused by erroneous impressions on the mind.” 26 Take first non-culpable mistake. When is there civil liability? Mr. Salmond 27 says that "inevitable" (by which he means nonculpable) "mistake is commonly no defense at all" against civil liability. Later, page 14, he adds: "To this general principle of absolute liability for mistake the law recognizes a few exceptions of minor importance... One of the fullest and ablest discussions of this topic is the article by Professor Whittier.28 Looking at the question as a matter of principle, the learned writer thinks that the general rule should be that non-negligent mistake of fact constitutes a defense to civil liability. But he regards the weight of authority as contra. As to damage to the person, he recognizes that there is a seeming conflict of authority. He says: "On the one hand, we have certain instances. where the mistake is held no excuse; on the other hand, we have even more numerous sets of circumstances in which the defendant is 24 Professor Whittier, 15 HARV. L. REV. 336-37. 25 SALMOND, TORTS, 4 ed., 16. 26 2 EDWARD LIVINGSTON, COMPLETE WORKS ON CRIMINAL JURISPRUDENCE, 641. 27 TORTS, I ed., 12. 28 15 HARV. L. REV. 335-52. not held." And he believes "that no adequate distinction can be drawn between these two lines of cases." As to damage to person"As alty and realty, he says that the courts "almost invariably" refuse to sustain the defense of non-negligent mistake.29 Upon the general question we differ from Salmond, and to some extent from Whittier. It is true that, in many actions for intentionally intermeddling with property, the defense of non-negligent mistake has not been sustained. But in almost all the reported cases under this head the particular mistake set up was in regard to the title to the property. The defendant has alleged that he without negligence believed that the property belonged either to himself or to the person under whose authority he was acting. The cases overruling this defense are regarded by us as deciding only that a mistake concerning this particular subject, i. e., a mistake concerning title, does not avail as a defense.30 These particular cases do not decide whether mistakes on other subjects do, or do not, constitute a defense to actions for damage to property or to the person. We do not think that there is any general rule as to whether nonnegligent mistake does, or does not, exonerate from civil liability. Each particular set of cases seems to us to be decided upon the special reasons of policy or expediency bearing upon that particular set of facts.31 Although two rights may be of equal intrinsic value, yet the efficient protection of one right may require the allowance of conduct which would not be so necessary to the protection of the other right. The nature of the particular right to be protected affects the method of protection to be allowed by law. Consider now cases of non-culpable accident. Here non-liability is the general rule.32 29 See 15 HARV. L. REV. 339, 340, 341, 342, 347. 30 Professor Whittier earnestly argues that this doctrine as to title is wrong on principle, but he admits it to be supported by an overwhelming weight of authority. See 15 HARV. L. REV. 343-47. As to the inexpediency or injustice of this doctrine, we are unable to concur with Professor Whittier. 31 This view explains some alleged inconsistencies in the decisions relative to damage to the person, pointed out in 15 HARV. L. REV. 341-42.. 32 "Pure accident will hardly seem to any one who is not a lawyer to be a special ground of exemption, the question being rather how it could ever be supposed to be a |