36 W. B. Taylor— Recent Researches in Sound. 



of the noise from the cataracts of the Orinoco, at a place on the 

 Atares, to the unequal heating of the air and the reflection and 

 dispersion of the sound from the surfaces of the striae of differ- 

 ing density. 



[Gr.] It was further noticed by General Duane that " when 

 the sound is thus impeded in the direction of the sea, it has 

 been observed to be much stronger inland ;" tending to confirm 

 his idea that the sound in passing from a warmer to a cooler 

 region of air " undergoes reflection at their surface of contact." 

 (p. 104.) 



Professor Henry dissents from this opinion that the extinc- 

 tion of powerful sounds is due to unequal density of the at- 

 mosphere. Admitting that " a slight degree of obstruction of 

 sounds may be observed" from such a condition, he thinks it 

 " entirely too minute to produce the results noted." (p. 104.) 

 He believes that the " true and sufficient cause" is the differ- 

 ence between the upper and lower currents of air, which tends 

 to bend the sound rays either upward or downward, as sug- 

 gested by Professor Stokes in 1857. He adds, " In the com- 

 meuts we have made on the Eeport of General Duane the in- 

 tention was not in the least to disparage the value of his results 

 which can scarcely be too highly appreciated." (Rep., p. 106.) 



[H.] A difficulty occasionally observed with vessels in a fog, 

 is an apparently false direction of the audible signal ; which 

 General Duane regards as "due to the refraction of sound in 

 passing through media of different density." (p. 104.) 



[I.] While thus adopting "the conclusion that these anomalies 

 in the penetration and direction of sound from fog-signals, are 

 to be attributed mainly to the want of uniformity in the sur- 

 rounding atmosphere,*' General Duane was also led from obser- 

 vation and experiments to believe " that snow, rain, fog. and 

 the force and direction of the wind, have much less iufluence 

 than has generally been supposed." (p. 104.) This is in confir- 

 mation of his previous observation [C]. 

 III. 



Professor Tyndall commenced his investigations on fog-sig- 

 nals on the 19th of May, 1873, "at the instance of and in 

 conjunction with the elder brethren of the Trinity House," as 

 the scientific adviser of the Corporation. 



[1.] On May 20, 1873, observations showed the relative pene- 

 trating power of different instruments to be variable. At six 

 miles the fog-horn was inaudible, while an eighteen pound 

 gun with three pound charge was heard for ten miles. On 

 many subsequent occasions tbe horn was found to be superior 

 to the gun. {Trans. R. S., p. 188.) Occasionally the whistles 

 were superior to the trumpet, though not generally so. (p. 189-) 



