UNDULATORVY MOVEMENTS AS AFFECTING OUR SENSES. 153 
In the case of the ear it is generally agreed that two things are 
necessary for the production of physical sound, viz.: A vibrating mass of matter, 
and an elastic medium to transmit the vibrations to the organ of hearing. ‘There 
can be no physical sound in a vacuum. The undulatory motion in this case is 
composed of to-and-fro elements, i. e. there is alternate condensation and rare- 
faction among the particles of the transmitting medium. The limits of rate of 
vibration are about 16 per second for lowest and about 40,000 for highest. Below 
16 per second the rate is so slow that the ear is not affected, and above 40,000 so 
fast that the ear fails to take cognizance of them. The ear is the only one of the 
organs of sense that is a‘fected by aérial vibrations. 
It is well known that the earliest theory of vision was the cor- 
puscular. It was said that exceedingly small particles shot from the luminous 
body fell upon the eye and produced vision. Sir Isaac Newton and others were 
apostles of this theory. Nowadays we laugh at such an idea. Let us think of a 
particle sent from the sun. No matter how small it would be, it might acquire 
velocity enough to give it a momentum that would destroy the eye when it fell 
upon it. M dern science has adopted another theory known as the undulatory. 
This presupposes an exceedingly rare medium pervading all space and occupying 
the interstices between molecules and atoms. This medium is called ‘‘ Ether.” 
In the case of sound, the wave motion was the result of mass vibration upon the 
air; but in case of light, the wave motion is the result of molecular vibration upon 
this so-called ether. The elements of the undulatory motion have a transverse 
movement just as in the case of water waves or the waving of a field of grain. 
The effect produced upon the eye will vary with the number of waves entering 
it in a given time. It has been found by calculations based on observations 
made on soap bubbles, etc., that to produce the sensation we call ved, over 400 
trillions of waves must enter the eye in one second. Then as the numbers 
increase the impression experienced by the eye varies through all the colors of 
the rainbow until about 700 trillions per second are reached. Beyond that the 
eye fails to be affected and darkness reigns, just as it did before reaching the 400 
trillions just now mentioned. Now it is well known that light is usually the 
result of great heat. Hence we may naturally conclude that below 400 trillions 
and down to an unknown limit the effect of molecular movement is to produce 
waves in ‘‘ether’”” which affect the papillae of the skin and make the sensation 
we call heat. When two bodies are brought near each other, if we keep in mind 
that the molecules of each are in motion, then that will be the hot one whose 
molecules are moving the faster and producing the greater number of ethereal 
undulations in a second. But what shall we say of the effects of rates of vibra-- 
tion beyond the highest extreme of impressions named light? We know not 
unless they are such as affect the motor nerves and the muscles and produce the 
sensations we ascribe to electricity. And were we incliued to materialism we 
might say that certain rates of inconceivable rapidity give rise to thought, spirit, 
life, etc. Be that as it may, let us now come back to our special organs of sense 
