I am summoned to attend your Committee on Friday, and as it is known that I have expressed opinions favourable to the Atmospheric System, and that I am actually applying it upon a line of some length, it would be considered an absurd affectation, and would, moreover, be useless to attempt, to avoid giving evidence when so called upon; but I am a most unwilling witness. I think it rather hard upon a professional man, who wishes to be cautious and prudent, that he should be called upon to express general opinions, which, if written even in the most studied and careful language, cannot be so worded as to be applicable to every case that may hereafter arise, or to be proof against the unfair and unscrupulous attack of the paid writers on these controversies. I mention these difficulties, which I feel that you may make some allowances for, if my feelings should appear in my evidence, or if that evidence should appear to fall very short of the opinions I am known to entertain, and which I must entertain to induce me to apply the system extensively, as I am doing. I find it difficult to define the points upon which it would be desirable to examine engineering witnesses, and I really believe that, entering freshly upon the subject and feeling as one of the public, you are more likely to elicit the useful points than one who, like myself, has been turning his whole attention (lately, at least) solely to the mechanical construction. However, I enclose a copy of a letter I addressed to a party interested in the patent, which refers to my opinions on the several points--opinions, however, expressed without that caution to which I referred as so necessary. (_Enclosure._) March 31, 1845. I object very much to giving evidence upon the abstract point of the applicability of a particular system, and thus furnishing general opinions which others are to apply as they may choose to particular cases; and if I could, I would refuse to give evidence at all before the present Committee, whatever might be the consequence to the promoters of the Atmospheric System. Circumstances, however, render such a refusal impossible; but I am equally anxious not to be drawn into becoming an advocate of a system. When I gave evidence last year,[67] although it was then very much against my inclination, it was in support of a particular case; and it was only incidentally that my opinion was advanced as to a system. The evidence is now avowedly sought in support of a system, and I do not, as I before stated, intend to become an advocate of this or any other system. I mention these my views to prevent disappointment. If the following facts and opinions are likely to be of use to the Committee, I can give evidence on them.