1874.| Atomic Matter and Luminiferous Ether. IgI 
There appears no difficulty in appreciating the very precise 
equality of two distin¢t but otherwise identical musical 
notes. We can understand that two bodies may make the 
same number of vibrations in a second, and that two sounds 
may be identical, excepting in order of time. We can under- 
stand that the vibrations of light and heat of two distinct lines 
of rays may be of the same length, amplitude, and frequency, 
and so give the same appreciable results of light, colour, 
temperature, and mechanical force. 
When, however, we examine natural objects, we never find 
two alike; there is always an observable difference. In this 
sense the multitude of individual faéts is overwhelming; 
and two natural objects, whose only difference is that they 
occupy different portions of space, or occur at different 
times, are unknown. ‘There are differences between two 
tuning forks, each sounding the same note. We must 
conclude that, as each fork changes with use and time, so it 
has changed between two soundings, although its sounds 
may remain unaltered. 
Different but otherwise identical vibrations of sound and 
light have been compared, and have always been found to be 
the same ; whilst all attempts to prove or to obtain perfect 
resemblance between any two solid, or, so to say, natural, 
objects, have been failures. Hence, identity of all active 
properties is more probably due to identity of motions than 
to identity of quantities or forms of the substances. 
Adding to these conclusions the almost axiomatic idea 
that all force is motion, the enquiry, as to the necessity for an 
elastic ether, is restricted to the capacity of tangible or 
atomic matter for conveying vibrations of all kinds. 
It is unnecessary for this purpose to discuss the question 
as to the definite size of a molecule, defining that term as 
the smallest portion of a substance that will produce the 
phenomena, whereby the individuality of the substance is 
recognised. There is no @ priort reason why that molecule 
should not be of a definite size in comparison with the 
definite number and kind of vibrations it has to originate or 
transmit, and by which alone its characteristics are recognised. 
Sound is not produced by one movement, but by a series 
of movements, and one movement alone is inaudible. 
Similarly it is probably true that all observable phenomena 
of this kind are due to a not indefinite succession of 
vibrations. Mentaily, we can isolate each vibration, but 
practically no single vibration can produce a manifest 
phenomenon, such as we call sound, light, heat, or the like ; 
and as one of the results of all chemical action is measured 
