As late as 1870 the Speaker occasionally took part in debate, when the House was in Committee of the Whole where he does not preside;[262:2] but it would now be thought inconsistent with his position of absolute impartiality to speak or vote in committee. He therefore never votes unless he is obliged to do so by a tie occurring when he is in the chair. It is commonly said that he always gives his casting vote in such cases so as to keep the question open; but this is not strictly true. When, however, his vote involves a final decision, he bases it, not upon his personal opinion of the merits of the measure, but upon the probable intention of the House as shown by its previous action, or upon some general constitutional principle;[262:3] and it may be added that the chairman of a Committee of the Whole, when called upon to break a tie, follows the same practice.[262:4] The chair in Committee of the Whole is regularly taken by the Chairman of the Committee of Ways and Means--commonly called for that reason the Chairman of Committees--who, like the Speaker, withdraws, on his appointment, from political contests, speaking and voting in the House nowadays only on questions relating to private bills. He is nominated at the beginning of the Parliament by the ministry, from among their prominent supporters, and retires from the position when they resign. Considering that his duties consist in presiding, like the Speaker, with strict impartiality, and in a purely non-partisan supervision of private bill legislation, it is somewhat strange that he should go in and out of office with the cabinet, but in fact one hears no criticism of his conduct on that score, largely, no doubt, because he always takes the Speaker as his model. Since 1855 he has acted as deputy speaker, when the Speaker is unavoidably absent,[263:1] and in order to prevent any possible inconvenience from the absence of both of these officers from the House, or of the Chairman of Ways and Means from the Committee of the Whole, provision was made in 1902 for the election of a deputy chairman who can fill the vacant place.[263:2] [Sidenote: Other Officers of the House.]