88 THE POPULAR SCIENCE MONTHLY. 



not correct the error of the ear — in fact, many people seem to be 

 unaware that they have any inability to locate sound by the ear 

 until they have learned the fact by experience, and even then 

 they appear to consider marked instances as abnormal. 



It is sufficiently easy to account for aberrations of audition 

 as to the direction of sound from objective causes, such as reflec- 

 tion, diffraction, and deflection of sound-waves. But it may 

 also often be accounted for by what Prof. Henry called subject- 

 ive causes, such as induce belief that an anticipated sound has 

 come from a specified direction, when it has really come from 

 quite another direction. Here the personal equation of the list- 

 ener must be largely taken into consideration. The success of 

 the ventriloquist may also depend upon subjective causes. 



President Welling tells us something of how Prof. Henry, 

 when at Princeton, induced subjective causes in his pupils, to 

 their bewilderment, making them believe, for the moment, that 

 a given sound came from a specified corner of the class-room, 

 when it really came from quite a different direction. 



Mariners are beginning to accept the fact that they may err in 

 assigning the true direction to sound ; but their ideas on the sub- 

 ject are still vague and indeterminate. Hence occur collisions be- 

 tween ships at sea, and lawsuits between their owners on shore. 

 The collision at 10 P. m., on September 21, 1882, between the 

 Dutch steamer Edam and the British steamer Lepanto, on 

 George's Bank, Atlantic Ocean, when the former was sunk by 

 the latter, resulted in a suit in the United States District Court 

 at New York city, in which the case turned on an erroneous 

 location of the Edam by the Lepanto, on hearing the sound 

 of her fog-horn. The court dismissed the case with costs, hold- 

 ing that " an error of five points in locating a vessel's position 

 by the sound of her whistle in a fog is not necessarily a fault 

 under the proved aberrations in the course of sound." The 

 judge, in his decision, quotes, among others, papers read before 

 the Washington Philosophical Society as his authority for cer- 

 tain statements he makes as to these laws of sound bearing on 

 the case.* 



As it seems evident that the unassisted ear is likely to err 

 in determining the location of sound, the question arises, Can 

 the ear be aided in this matter ? Apparently this is possible. 

 Prof. Mayer, of the Institute of Technology at Hoboken, N. J., 

 has, to a certain extent, solved this problem by the construction 

 of an instrument called the " topophone," by the use of which 

 President Morton, a member of the Lighthouse Board, was en- 

 abled to locate within ten degrees, or less than one compass- 

 point, the sound of a fog-signal, when in the cabin of a steamer 



* See " Federal Reporter," October 28, 1884, p. 651, 



