When anyone purchases land he estimates its probable value and takes the risk of increase or diminution. If a railway station is opened adjacent to his land, its value will go up if a factory is built on the next plot, it may go down. In one case benefit and in the other injury results but the fact that these risks may work hardship does not prevent either the station or the factory from coming and there seems no reason why the community should refrain from putting upon the use of land for building purposes a limitation of the number of houses to the acre, because this may diminish the value of certain pieces of land and increase that of others. Indeed, there is another point of View which might be put with some force by those who have purchased land a little farther out of the town. May it not be put thus A. Has purchased land on the assumption that the overcrowding of buildings would continue to be allowed long enough for him to develop it. If, in the interests of public health, that overcrowding is forbidden, he has simply made a mistake in his speculation, and he loses thereby. But can he really claim that there is any injustice For B., who has purchased some other land a little further out, has calculated that the general tendency to check overcrowding which has marked the development of by-laws for some time past, would, at an early date, bring a building value to his land, and he will be a loser if overcrowding continues. Could he not, with equal force, say that it is very unjust to him that so many houses should continue to be allowed to be built to the acre that building value is prevented from reaching his land, a value which would accrue to it if such overcrowding were prevented, as it ought to be in the public interest. It seems to me that in matters of this kind it is the obvious duty of the community to provide for the right system of development, and not to be turned aside because of hardships that may fall upon a few individuals who have laid their plans on the assumption that they would continue to be allowed to do something which has proved to be detrimental to the community. The fact is that nobody can acquire a prescriptive right to injure the community.