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Rh of his country. Such, if I dare say so, are the sentiments which I have ever expressed regarding Prof. Henry here and elsewhere.

When I first learned that he was in danger of falling into what I considered to be grave scientific error, I went as far as friendliness dared go to avert it. I addressed to him a private letter, in which I tried to impress upon him the completeness and conclusiveness of the evidence which he seemed disposed to call in question. He did not honor that letter with any notice, preferring to discuss the subject publicly in the "Report of the Washington Lighthouse Board." He was clearly within his right in doing so; but I submit that I only exercised my right when I met him on ground thus chosen by himself.

No English gentleman that I have consulted can discern in what I have written any violation of the dignity of scientific debate; but your article would lead to the inference that I had both violated common honesty and taken leave of common-sense. I will not quote your words, because I cherish the hope that when you have reflected on them you will regret them. When I say "you," I mean the editor of the Nation, whose acquaintance I had the honor to make, and whose kindness I had the privilege to experience, in New York—I do not mean the writer of the article. Let me respectfully assure you, then, that, when I spoke of being "deflected by authority," "Prof. Henry's solution of ocean-echoes" was not at all in my mind, nor his "ruin," partial or total, in my calculations. Consider, I pray you, how impossible it is that this could have been the case. The "deflection" spoken of is expressly described as occurring at the outset of an investigation begun in May, 1873, whereas the Washington report containing Prof. Henry s solution of ocean-echoes is the report for 1874, which did not reach Europe until the spring of 1875. This, then, is the crumbling foundation on which your critic builds his odious charge. In verity, the remark on which he pours his peroratory invective was not meant for "laudation" of any kind, but merely to show the "polar" character of authority—its good side and its bad.

It is easy, as you know, Mr. Editor, to sneer and to assail; but less easy to show, without going into details not worth the labor, that the sneer is unmeaning, and the assault unfair. Nevertheless, the broad lines on which, in the present instance, I would meet my anonymous assailant may, I think, be made clear. He industriously mixes together things which ought to be kept apart—experiments on fog-signals and inquiries into "the causes which affect the transmission of sound through the atmosphere." The "blank" which I proposed to fill is stated, with unmistakable clearness, to have reference solely to such "causes." Neither Herschel nor Robinson, as far as I know, ever made an experiment on fog-signals; still I quote them. Why? Because they are the most eminent and authoritative exponents of the theories of acoustic opacity which up to last year were entertained