The words "public authority" are in frequent use, but they do not appear to have been the subject of any clear definition. It is an expression used as a very general designation of a diversified class of bodies concerned in carrying out public functions. We speak of a highway authority, a sanitary authority, a water supply authority, a lighting authority, a harbour authority, a tramway authority, a transport authority or a railway authority, and in relation to railways or tramways where a different body is charged with construction we speak of a construction authority. Without much consideration of what common characteristics all these possess or how much further the expression will go, we speak of public authorities to embrace these and many other bodies carrying on public functions. A well-known legal text book, Robinson on Public Authorities, takes its title from the term, but a definition of the term will not be found in the work. It would appear by inference, however, that the Crown itself is considered by the author to fall within the expression, that it extends to the Ministry of Health, to municipal corporations, to the Postmaster-General, to the guardians of the poor, to educational authorities, to the trustees of turnpike roads, to health authorities and to various local and municipal bodies. In England the expression is employed as the title to the Public Authorities Protection Act 1893. That Act is the subject of much case law and if it were not for the fact that the application of the Act depends rather on the character of the powers, duties and functions exercised or fulfilled than upon the classification of the bodies concerned, the judicial decisions might have proved a guide in the determination of the present case.