ing frequencies, and the higher rates of vibration are so intense that the mind can scarcely conceive them. When we think of 767 trillions of vibrations per second, it has little definite meaning to the lay mind; yet science has devised means to accurately determine so high a rate, which represents the extreme violet of the spectrum, and is the highest rate of vibration which our eyes are capable of detecting. The lowest rate of vibration to which our eyes are sensitive is 392 trillions per second, which represents the extreme red of the spectrum.
Our eyes are sensitive to all the other rates of vibration between the extreme violet and the extreme red and all these complex waves, acting together, produce what we call daylight. The waves which produce a sensation of light when they fall upon the eye are, naturally, called light waves, although the photographic plate is affected by light waves which are outside the rates of vibration to which the eye is susceptible.
When the ether waves impinge upon a body of ordinary opaque mass, it may be warmed, the energy being transformed into heat. While the light waves may produce heat, there are also ether waves called dark heat waves, which come at a rate of vibration much too slow to produce a sensation of light.
We say that glass is transparent because it does not appreciably obstruct the ether waves. We may sit near a closed window and enjoy the warmth of the sun because the glass, being transparent, does not arrest the ether