The opinion
Justice Lummus
concurs in the result, but on a simple ground which can be stated briefly. A presumption is a rule of law which compels the conclusion that a fact exists, in the absence of some required quantity of evidence or degree of proof to the contrary. It is impossible to weigh a rule of law, or to attribute to it persuasive force as evidence of a fact. Therefore the opinion states what is now settled law in rejecting the theory that a presumption is evidence. Upon any other theory of presumptions that to his knowledge has ever been advanced, a presumption can have no greater effect than to control unless rebutted by proof to the contrary. Except for the presumption of legitimacy, most authorities give a presumption less effect. When the statute cast upon the defendant the burden of proving by a preponderance of the evidence contributory negligence on the part of the plaintiff, it did everything for the plaintiff that a presumption of his due care could do, and according to most authorities on the subject of presumptions it did more. The statutory presumption of due care, therefore, is wholly overshadowed by that burden of proof, and can have no practical effect. If it never had been created, or should be abolished, neither party would be a whit the better or the worse. The statutory presumption of due care is like a handkerchief thrown over something covered by a blanket also. Lisbon v. Lyman, 49 N. H. 553, 563. Board of Water Commissioners v. Robbins, 82 Conn. 623, 640 . For this reason, if the burden of proof is correctly stated to the jury, there can be no reversible error in dealing with the presumption of due care, whether the judge adopts what seems the better course of refusing to mention it at all, or, as the judge did in this *197 case, indulges in what must needs be an academic discussion of its theoretical operation; and this, no matter whether that discussion conforms to the true theory of presumptions or not. Since the simple ground which has been stated requires the overruling of these exceptions, and we are dealing with a so called presumption which has no operative effect and only a verbal or theoretical existence, a discussion of the working of genuine presumptions would be superfluous.