This great advantage of stationary over locomotive power was a sufficient justification for introducing a system which promised to realise it to any considerable extent; although many difficulties might have to be encountered. As has been already stated, Mr. Brunel had satisfied himself that the Atmospheric System was theoretically economical, and that its trial at Dalkey had shown that it was practically free from mechanical objections. Mr. Stephenson, indeed, had admitted that the mechanical details had been brought to a remarkable degree of perfection; but this admission was not any qualification of the radical difference of opinion which existed between him and Mr. Brunel, to which Mr. Brunel drew attention in his report of August 1844. The subsequent abandonment of the Atmospheric System led many to believe that Mr. Brunel had been rash in rejecting the detailed investigations and conclusions of Mr. Stephenson, and that the adverse conclusions which Mr. Brunel had refused to entertain were subsequently established. But, in fact, the failure of the Atmospheric System was due to failure in some of its mechanical details, and was not due to those inherent defects in its principle which Mr. Stephenson in his report considered that his experimental data had established. Mr. Brunel’s opinions were again brought prominently into notice in the evidence given by him before a Select Committee of the House of Commons, which was appointed in the Session of 1845, in consequence of the number of projected lines which it was proposed to work by the Atmospheric System. The following letter, written by Mr. Brunel to one of the members of the Committee, explains what he considered to be his position at this time:-- April 3, 1845.