Circles in water, sound in air, and images to the eye
The stone thrown into water compared with the circular spread of sound and vision
This text sheet develops Leonardo's analogy between waves in water, sound in air, and the transmission of images to the eye. A stone striking the surface of water makes circles that widen until they are lost, and the air struck by a voice spreads sound in the same circular way, so that the nearer listener hears better than the farther. A small diagram of crossing visual rays at the right supports the further claim that no body is so large that at distance it does not subtend a smaller visual pyramid than a small near object.
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Circles in water and sound in air
A stone thrown into water becomes the centre of various circles whose centre is the place struck, and these circles widen until lost. Likewise the air fills with circles whose centres are the sounds and voices made in it, so that the nearer one hears better and the farther one hears less.
Sound reaching equidistant ears
Just as the stone in water is the centre and cause of various circles, sound behaves so in the air, sending its voice equally to equidistant ears and spreading circularly, showing the place struck as its centre.
The visual pyramid and images to the eye
No body is of such magnitude that at a long distance it does not appear by a smaller pyramid than a small near body, so it seems smaller to the eye than the smaller nearer object; thus the images of bodies are spread circularly through the infinite parts of the nearby air. A small figure of crossing visual rays illustrates the point.