The plaintiff's exception must, therefore, be overruled, for since the defendants have accepted the provisions of Laws 1911, c. 163, the burden is on him to show that his ward neither knew nor ought to have known of, and appreciated the risk incident to the defect in the defendants' instrumentalities of which he complains. Bergeron v. Company, ante, 231; Smith v. Company, ante, 299; Cassidy v. Company, 79 N.H. 427; Merrill v. Company, 79 N.H. 211; Proulx v. Goodrich, 77 N.H. 297; Dionne v. Company, 76 N.H. 17; Fontaine v. Company, 76 N.H. 163; Sanborn v. Railroad, 76 N.H. 523; Ahern v. Company, 75 N.H. 99; Gorman v. Company, 75 N.H. 123; Manley v. Railway, 75 N.H. 465; Cronin v. Company, 75 N.H. 319; Smyth v. Company, 75 N.H. 403; Hicks v. Company, 74 N.H. 154; Roy v. Hodge, 74 N.H. 190; Murphy v. Railway, 73 N.H. 18; Hilton v. Railroad, 73 N.H. 116; St. Jean v. Tolles, 72 N.H. 587; Boyce v. Johnson, 72 N.H. 41; O'Hare v. Company, 71 N.H. 104; Allen v. Railroad, 69 N.H. 271; Young v. Railroad, 69 N.H. 356; Casey v. Railway, 68 N.H. 162; Collins v. Company, 68 N.H. 196; Nourie v. Theobald, 68 N.H. 564. Exception overruled.