The case was decided in favour of the plaintiff, on the presumption of a lost grant.

Concerning the degree of purity which a man may reasonably expect to find in the air which reaches his building, and the cases in which he may successfully take action against his neighbour for nuisance, or the cases in which a man may successfully assert and maintain a privilege by way of easement to pollute the air to an unusual extent, there is much room for conflict of opinion in different cases which may arise.

The right to purity of air, though a natural common law right, is from the nature of things one of degree only. No one has a right to demand that the air which reaches his tenement over the lands of others shall be absolutely pure. There is no such thing as absolutely pure air to be found anywhere in nature, and certainly not in inhabited regions, and no exact standard of purity can be prescribed concerning such a variable mixture as air, so that the natural right cannot extend beyond a right to air in a reasonably usable and enjoyable condition, and even when it is not in a wholesome condition for breathing or other uses, no man has a right of action against any other merely on that account, unless the person against whom the claim is made has been responsible for lowering its standard of purity or usefulness to an actionable extent. Speaking generally, every animal, dead or alive, and all vegetable matter detached from the earth, and all combustion, must tend continually to pollute or spoil the atmosphere in the neighbourhood, more particularly in regions where moisture abounds, so that all people living or working in the neighbourhood must suffer more or less from natural operations incidental to ordinary human and animal life and vegetable decay. All they have a right to demand is that the atmosphere shall not be polluted to an excessive or unnecessary extent by neighbours. They may object to anything which amounts to a nuisance. On the other hand, there are some trades and occupations which cannot be carried on without polluting the atmosphere to such an extent as to be a nuisance to neighbours.

In such cases an easement to pollute the air may sometimes be acquired by prescription under the old common law, though not under the Prescription Act, which is silent about air, and under which no easement of air can be obtained. An easement to pollute air may also be acquired by grant, but it is evident that unless the circumstances are very exceptional (such, for example, as when the original grantor owns all the land surrounding the tenement of the grantee for a considerable distance in all directions) a grant by one neighbouring owner will confer no rights as against any other neighbours or over their lands.

Hence actual or implied grants are not so frequently relied upon to establish an easement to pollute air as in cases where light and most other easements are in question. Prescription use and enjoyment under the old common law, with the old presumption of lost grants, will give a good title as against the whole surrounding neighbourhood, and this is the most usual means by which a privilege to carry on offensive trades may be gained.

It is so exceedingly difficult as to be practically impossible to lay down in explicit and exact terms how far and when an owner may pollute the air in his neighbourhood with impunity, and the exact circumstances under which a neighbour may be able to establish a cause of action, and to succeed in court, and to what extent and what remedies should be applied. To a very large extent the practice of offensive trades or manufacturers is a matter of general public interest, and in modern days dangerous and offensive trades are to a considerable extent brought under regulation and controlled by supervision in the public interest. Private owners of neighbouring property have, generally speaking, a right of action if there is a real nuisance of a character to cause depreciation of their property, and they may be able to obtain substantial relief in the shape of damages, and perhaps sometimes an injunction, if their own conduct in the matter has been reasonable, and if they have not acted in such a manner that acquiescence might be implied. The rights and conduct of all parties before the Court may be relevant to the inquiry, and to the remedies in these cases of nuisance, and even when a defendant carrying on an offensive trade is able to show a prescriptive right of easement relating to the pollution of air as a necessary consequence of carrying on the trade or manufacture, it may still be a question whether the degree of pollution is more than is impliedly covered or protected by the easement.

There is this peculiarity about an easement to pollute air, that the easement secures to the dominant owner a right to pour offensive material into the atmosphere at large, and the dominant owner has no subsequent control over its distribution, nor any certain knowledge of the direction in which it may be carried, or how far, so that it is no easy matter to say which are servient tenements, and to what extent they are so. Also, the height at which effluvia are discharged into the atmosphere must in most cases materially affect the distribution.

Neighbours may therefore be concerned with structural alterations in factories and chimneys, and with changes in the processes which are carried on inside, so that in these days, when changes in processes and enlargement and alteration of factory buildings are so numerous and progressive, disputes may easily arise where the main question will be whether the action of the factory owner is of a character to inflict unjustifiable injury on neighbouring property, and on the owners and occupiers.

The proportion of cases in which an easement can be successfully pleaded by way of defence will probably be very small, and the rights and remedies of parties will for the most part be determined on the merits of each case.

It may here be noted that real injury to property, or real injury to health, actual or immediately threatened, must form the basis of complaint. Courts will not lightly interfere with the reasonable practice of any legitimate trade, except for good cause shown, and a fastidious taste or personal dislike of particular smells, which are not seriously unwholesome or dangerous to health, will not be accounted as giving a good cause of action against a neighbouring owner who acts reasonably and within his natural rights. For example, a householder may not like to have a butcher or fishmonger open a shop in his immediate neighbourhood, but if the business is carried on in a generally reasonable manner applicable to such shops, the dissatisfied neighbour will ordinarily have no cause of action for nuisance. On the other hand, if any man carries on a trade which is really a nuisance to neighbours, he cannot successfully plead, by way of defence, that the air in the neighbourhood was otherwise seriously polluted before he began to pollute it. The fact that other people are habitually committing nuisances in the neighbourhood does not justify the commission of a fresh nuisance by him if a neighbour objects. Also, a man carrying on an offensive trade or occupation cannot successfully defend an action for nuisance by merely pleading that the air was habitually polluted before the plaintiff came into the neighbourhood, - or in other words, that plaintiff has voluntarily come within range of the nuisance which would not otherwise have affected him. A man cannot merely, as first comer in a neighbourhood, originate a nuisance, and then insist that every new comer shall put up with its continuance. Each new comer will ordinarily be vested with a natural right to have unpolluted air to breathe and to use in other ways, and prima facia has good ground of action against anyone who seriously infringes that natural right ; and the person causing the nuisance can only justify by proving an easement, unless there exists some special personal reason why plaintiff should not be allowed to assert his natural right. Ordinarily, uninterrupted pollution for a full period of twenty years at least at the same place, in the same manner, and substantially to the same extent, will suffice to establish an easement if the practice has been continued all that time in a manner capable of being resisted, and if it has not been resisted. It may, however, be nearly always questioned how far and to what extent and when such easements can be held to be established.