704 THE POPULAR SCIENCE MONTHLY. 



at a distance of 2 miles ; in the great majority of cases it may be relied 

 upon at a distance of 3 miles, and in the majority of cases to a distance 

 greater than 3 miles. 



Happily the experiments thus far made are perfectly concurrent in 

 indicating that at the particular time when fog-signals are needed, the 

 air, holding the fog in suspension, is in a highly-homogeneous condi- 

 tion ; hence it is in the highest degree probable that in the case of fog 

 we may rely upon the signals being effective at far greater distances 

 than those just mentioned. 



I am cautious not to inspire the mariner with a confidence which 

 may prove delusive. When he hears a fog-signal he ought, as a gen- 

 eral rule (at all events until extended experience justifies the contrary), 

 to assume the source of sound to be not more than 2 or 3 miles dis- 

 tant, and to heave his lead or take other necessary precautions. If 

 lie errs at all in his estimate of distance, it ought to be on the side of 

 safety. 



With the instruments now at our disposal wisely established along 

 coasts, I venture to think that the saving of property in ten years will 

 be an exceedingly large multiple of the outlay necessary for the estab- 

 lishment of such signals. The saving of life appeals to the higher mo- 

 tives of humanity. 



In a report written for the Trinity House on the subject of fog-sig- 

 nals, my excellent predecessor, Prof. Faraday, expresses the opinion 

 that a false promise to the mariner would be worse than no promise 

 at all. Casting our eyes back upon the observations here recorded, 

 we find the sound-range on clear, calm days varying from 2% miles to 

 16^ miles. It must be evident that an instruction founded on the lat- 

 ter observation would be fraught with peril in weather corresponding 

 to the former. Not the maximum but the minimum sound-range should 

 be impressed upon the mariner. Want of attention to this point may 

 be followed by disastrous consequences. 



This remark is not made without cause. I have before me a 

 " Notice to Mariners," issued by the Board of Trade, regarding a fog- 

 whistle recently mounted at Cape Race, and which is reputed to have 

 a range of 20 miles in calm weather, 30 miles with the wind ; and in 

 stormy weather or against the wind 7 to 10 miles. Now, considering 

 the distance reached by sound in our observations, I should be willing 

 to concede the possibility, in a more homogeneous atmosphere than 

 ours, of a sound-range on some calm days of 20 miles, and on some 

 light, windy days of 30 miles, to a powerful whistle; but I entertain a 

 strong belief that the stating of these distances, or of the distance 7 

 to 10 miles against a storm, without any qualification, is calculated to 

 inspire the mariner with false confidence. I would venture to affirm 

 that at Cape Race calm days might be found in which the range of the 

 sound will be less than one-fourth of what this notice states it to be. 



