484 THE POPULAR SCIENCE MONTHLY. 



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 afiected the optical clearness of the atmosphere. Prior 

 to the South Foreland investigation, where, I would ask, is a " sys- 

 tematic 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 afiirmed 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 prac- 

 tical 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 Fore- 

 land. 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 npt, 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 afiect the trans- 

 mission of sound thi"ough the atmosphere." And, if I except the sa- 

 gacious 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 ofiicer 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 em- 

 phatic advice to the Elder Brethren of the Trinity House not to con- 

 fine 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 adoj^tion of others from Canada and the 

 United States. The siren^ for example which your critic erroneous- 



