Page:Transactions NZ Institute Volume 25.djvu/658

 sence of the rod, only the hand, which feels the strokes when brought within their reach. The vibrations become more rapid, till when they reach the number of thirty-two in a second a deep hum strikes my ear (that is to say, the tympanum is pressed sixteen times, and sixteen times withdrawn, therefore sixteen blows are received upon the ear). The tone rises continually in pitch, and passes through all the intervening grades up to the highest, the shrillest note; then all sinks again into the former grave-like silence. While full of astonishment at what I have heard, I feel suddenly (by the increased velocity of the vibrating-rod) an agreeable warmth, as from a fire, diffusing itself from the spot whence the sound had proceeded. Still all is dark. The vibrations increase in rapidity, and a faint-red light begins to glimmer; it gradually brightens till the rod assumes a vivid red glow, then it turns to yellow, and changes through the whole range of colours up to violet, when all again is swallowed up in night. Thus nature speaks to the different senses in succession—at first a gentle word, audible only in immediate proximity; then a louder call from an ever-increasing distance; till, finally, her voice is borne on the wings of light from regions of immeasurable space.

This passage bears out my idea that light and sound are convertible, the one into the other, through the medium of heat.

In another place Shellan says,—

"The gradation of colour from red to ultra-violet is to the eye what the gamut is to the ear, and it is not without reason that we talk of harmony of tone and colour. To the physicist the words 'colour' and 'tone' are only different modes of expression for similar and closely-allied phenomena; they express the perception of regular movements recurring in equal periods of time, in ether producing colours, in air musical sounds, &c."

In tracing the colours in the spectrum from red to ultra-violet we notice first the three primary colours, red, yellow, and blue. Between red and yellow orange is formed; between yellow and blue comes green; and above blue we find violet and ultra-violet, which last seems on the verge of running into the red again, just as the seventh note of the musical scale, or leading note as it is called, seems to want the octave, or repetition of the keynote, to follow it—in other words, it suggests it to the ear.

The colours in the spectrum are arranged as follows: Red, orange, yellow, green, blue, violet, and ultra-violet (some authorities name the last two indigo and violet).

Now I come to a very important analogy. If we take the proportion of increase in the number of vibrations in a second