of the Position of Sonorous Bodies: 62 5 
that joins his head and the place from which 
any particular sound proceeds. 
Though the fact I have been describing is 
established by universal experience, the cause of 
it, I believe, has never been investigated ; and 
indeed the question, when we first attend to it, 
seems to put on a very puzzling appearance. 
We know that when sound finds a free passage 
through the air, it takes the shortest path, lead- 
ing from its source to the person who attends 
to it; and that the sensation of hearing is occa- 
sioned by a succession of waves or pulses of 
air, which fall upon the auditory organs, in the 
direction of a right line drawn from the sounding 
body to the head of the hearer. But after the 
enquirer has arrived at this point in his exami. 
nation of the problem, his progress is hindered 
by the difficulty under consideration. The per- 
plexity here alluded to arises from the obscurity 
of the principle, whereby men compute the 
angles, which a right line, drawn from the place 
of a sound to the head of a hearer, makes with 
the two planes described above, as wellas their 
common section.—It is in vain to endeavour at 
an explanation of the phenomenon, by analogies 
borrowed from vision.—The spectator judges 
of the relative positions of visible objects, by 
knowing the situation which their images have 
on the retina, in respect to the axis of his eye; 
