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484 by the highest scientific minds. Theirs, moreover, and Arago's (not Prof. Henry's), was the "authority" which "deflected" me at first. Apart from the wind, the "causes" of acoustic opacity indorsed by these eminent men were rain, hail, snow, haze, and fog—everything, in short, that affected the optical clearness of the atmosphere. Prior to the South Foreland investigation, where, I would ask, is a "systematic inquiry" into these causes to be found? Surely, if such an inquiry has been published, it can be courteously pointed out and calmly discussed. If you can prove its existence you will have the right to demand from me the very fullest apology and reparation for stating that "no such systematic inquiry had to my knowledge been made." Even then I could not charge myself with untruth; for my "knowledge" was, and is, arithmetically what I have affirmed it to be; but I can confess ignorance and express regret.

Give me your patience while I endeavor still further to make this matter clear. As regards the invention of instruments and their practical establishment as fog-signals, so far was my knowledge behind "the science of the United States," that I had never seen or heard one of those great steam-whistles until I met them at the South Foreland. The common "siren" is well known to have been a familiar instrument with me, but the fog-signal I first saw and heard upon its native soil in America—not, however, as your critic puts it, but at the request, twice repeated, of Prof. Henry. Further, to the best of my recollection, prior to the month of May, 1873, I had only heard one or two experimental blasts from a fog-trumpet. In such work, then, I had neither part nor lot; and, if you will permit me to say so, though it is of the utmost practical value, I should hardly label such work with the name of "science." Quite apart from those practical achievements lies the inquiry into "the causes which affect the transmission of sound through the atmosphere." And, if I except the sagacious remark of General Duane which has been so curtly brushed aside, not a scintilla of light has been cast upon these causes by any researches ever published by the Lighthouse Board of Washington.

Will you allow me to say, in passing, that Major Elliot, the able and conscientious officer whose excellent "Report on the Lighthouses of Europe" was so displeasing to the board, did accept the invitation to Dover, and that to the present hour I feel indebted to him for the information and advice given to me at the time?

Upon my "conduct" and the knowledge which "influenced" it, your critic rings the changes of his wit. It is, after all, a very simple and straightforward matter. The "conduct" consisted in my emphatic advice to the Elder Brethren of the Trinity House not to confine themselves to home-made apparatus, but to include American ones in their inquiry. The subsequent trial led to the abandonment of the English instruments, and the adoption of others from Canada and the United States. The siren, for example—which your critic