2 6 
Dr. Young’s Lecture 
light, from the part of the retina on which it impinges : in the 
ear, wehave no other criterion than the slight difference of motion 
in the small bones, according to the part of the tympanum on 
which the sound, concentrated by different reflections, first 
strikes; hence, the idea of direction is necessarily very indistinct, 
and there is no reason to suppose, that different parts of the 
auditory nerve are exclusively affected by sounds in different 
directions. Each sensitive point of the retina is capable of re- 
ceiving distinct impressions, as well of the colour as of the 
strength of light; but it is not absolutely certain, that every 
part of the auditory nerve is capable of receiving the impression 
of each of the much greater diversity of tones that we can dis- 
tinguish ; although it is extremely probable, that all the different 
parts of the surface exposed to the fluid of the vestibule, are 
more or less affected by every sound, but in different degrees 
and succession, according to the direction and quality of the 
vibration. Whether or no, strictly speaking, we can hear two 
sounds, or see two objects, in the same instant, cannot easily be 
determined; but it is sufficient, that we can do both, without the 
intervention of any interval of time perceptible to the mind ; 
and indeed we could form no idea of magnitude, without a com- 
parative, and therefore nearly cotemporary perception of two 
or more parts of the same object. The extent of the field of 
perfect vision for each position of the eye, is certainly not very 
great ; but it will appear hereafter, that its refractive powers are 
calculated to take in a moderately distinct view of a whole 
hemisphere : the sense of hearing is equally perfect in almost 
every direction. 
