"At common law the office of constable or peace officer was regarded as a public office, and the holder of it as being, in some sense, a servant of the Crown. The appointment to the office was made in various ways, and often by election. In later times the mode of appointment came to be regulated for the most part by Statute, and the power of appointment was vested in specified authorities, such as municipal authorities or justices. But it never seems to have been thought that a change in the mode of appointment made any difference in the nature or duties of the office, except so far as might be enacted by the particular Statute. Again, at common law constables had large powers necessarily incident to the discharge of their functions as peace officers or conservators of the peace, amongst which perhaps the most important was the authority to arrest on suspicion of felony. To these powers others of a like nature have from time to time been added by statutory provisions, of which the 179th section of the Police Act is an instance. But there is no reason for thinking that the mere statutory addition to the list of their powers altered the essential nature of those powers. It seems also to have been always accepted as settled law that, although a peace officer was himself responsible for unjustifiable acts done by him in the intended exercise of his lawful authority, no responsibility for such acts attached to those by whom he was appointed.
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A consideration of the general doctrine of the law of agency as applied to the case of a constable leads to the same conclusion. In considering whether a master is liable for the acts of his servant the test is ... whether the party sought to be made responsible retained the power of controlling the act. Now, the powers of a constable, qua peace officer, whether conferred by common or statute law, are exercised by him by virtue of his office, and cannot be exercised on the responsibility of any person but himself. If he arrests on suspicion of felony, the suspicion must be his suspicion, and must be reasonable to him. If he arrests in a case in which the arrest may be made on view, the view must be his view, not that of someone else. Moreover, his powers being conferred by law, they are definite and limited, and there can be no suggestion of holding him out as a person possessed of greater authority than the law confers upon him ... A constable, therefore, when acting as a peace officer, is not exercising a delegated authority, but an original authority, and the general law of agency has no application."