RESEARCHES IN SOUND. 515 



nornena, are not mere matters of abstract scientific interest, bnt are of 

 great practical iinporfcauce, involving the secnrity of life and property, 

 since they include the knowledge necessary to the proper placing of 

 fog-signals, and the instruction of mariners in the manner of using 

 them. 



The hypothesis we have adopted, that of the change of direction of 

 sound by the unequal action of the wind ujion the sound-waves, is 

 founded on well-established mechanical principles, and offers a ready 

 explanation of facts' otherwise inexplicable. It is also a fruitful source 

 from which to deduce new consequences to be verified or disproved by 

 direct experiment. It would however ill become the spirit of true 

 science to assert that this hypothesis is sufiicient to explain all the facts 

 which may be discovered in regard to sound in its application to fog- 

 signals, or to rest satisfied with the idea that no other expression of a 

 general principle is necessary. An investigati^on however to be fruit- 

 ful in results, as a general rule, must be guided by ajyriori conceptions. 

 Haphazard experiments and observations may lead to the discovery of 

 isolated facts, but rarely to the establishment of scientific principles. 

 There is danger however in the use of hypotheses, particularly by those 

 inexperienced in scientific investigations, that the value of certain 

 results may be overestimated, while to others is assigned less weight 

 than really belongs to them. This tendency must be guarded against. 

 The condition of the experiment must be faithfully narrated, and a scru- 

 pulously truthful account of the results given. While we have used 

 the hypothesis above mentioned in the following investigations as some- 

 thing more than an antecedent probability, we have not excluded ob- 

 servations which may militate against it, and we hold oui'selves ready 

 to admit the application of other principles, or to modify our concep- 

 tion of those we have adopted, when new facts are discovered which 

 warrant such changes. But we require positive evidence, and cannot 

 adopt any conclusions which we think are not based upon a logical 

 correlation of facts. 



The investigations described in the following account, though sim^ole 

 {u their conception, have been difQcult and laborious in their execution. 

 To be of the greatest practical value they were required to be made on 

 the ocean, under the conditions in which the results ai^e to be applied to 

 the use of the mariner, and therefore they could only be conducted by 

 means of steam-vessels of sufficient power to withstand the force of 

 1 ough seas, and at times when these vessels could be spared from other 

 duty. They also required a number of intelligent assistants skilled in 

 observation and faithful in recording results. 



Observations in August, 1875, at Block Island. 



The party engaged in these investigations consisted of the chairman 

 of the Light-House Board; General Woodruff, U. S. A., engineer third 

 light-house district; Dr. James C. Welling, president of Columbian Uni- 



