3 
pressure, they are capable of acting dynamically on the solid 
organs of the ear, to which they are carried by the propaga- 
tion. The agitation thus communicated to the parts of the ear 
immediately acted upon by the aerial impulses, is eventually 
conveyed, through the auditory apparatus and nerves, to the 
brain, and there our investigation of the consequences of the 
initial disturbance comes to an end. It remains, however, to 
make the remark that this tracing of consequences does not 
lead up to the sensation which all the world calls sound, but 
is solely concerned with the material conditions, antecedent 
and concomitant, without which the sensation is not felt. 
4. This distinction, which has a very important bearing on 
the argument I propose to adduce relative to the destructi- 
bility of matter, has been much overlooked both by physicists 
and metaphysicians, and for some reason, which I do not 
understand, appears to be with difficulty apprehended. I 
called attention to it in the Introduction to my work entitled 
Creation in Plan and in Progress, published in 1861, where 
I have maintained, as I still do, that the sensation of sound 
is a faet of a certain class, but essentially different from the 
class of the facts, such as the pressure and vibrations of the air, 
under which, as material conditions, the sound is perceived. 
Just so, on the reasonable hypothesis that phenomena of 
light result from agitations of a universal ethereal medium, 
the sensations of light and colours are entities altogether 
diverse from the concomitant vibrations of the ether. So, 
also, the sensations of taste and smell are of a character not 
to be confounded with the materiality of the conditions under 
which alone they are felt. In short, it must be admitted, that 
in physics there are brought before us facts of two kinds, in 
such manner distinguished from each other, that whereas one 
kind cannot be dissociated from properties of matter, the 
other is certainly not material. Further, it may be asserted 
that co-ordinately with this distinction as to essence, there 
exists such correspondence between the two classes of facts 
that for every variation as to quality or degree in the material 
conditions, there is an analogous variation in the immaterial 
sensations, or vice versa. 
5. The foregoing separation of physical facts into two classes 
is a necessary preliminary to the argument that will be sub- 
sequently unfolded respecting the destructibility of matter. 
The argument will have to commence with establishing the 
position, already referred to in sec. 2, that physical science 
consists of two parts ; what is known by experiment merely, 
and what is derivable from the results of experiment by joining 
therewith results obtained by theoretical reasoning ; and that 
is 2 
