This Serpent being adorned with beautiful Colours, excuse a short Digression upon the Doctrine of Colours in Natural Bodies. Know then, Colours are the Children of Fire and Light.
I. Where there is Light, there is Fire; and Fire shews itself to be present by Light. The Sensation of Light is produced when the Particles of Fire, directed by the Action of the Sun, reach the Eye in right Lines. Now, Fire thus entering the Eye, gives a Motion to the optic Fibres at the bottom of the Eye, and thus excites the Idea of Light.
II. FIRE discovers itself by Colour; for all Colours depend upon Light, and Light depends upon Fire; and different Colours appear in Natural Bodies, as their Surfaces are disposed to reflect this or that sort of coloured Rays more than others. Colour is a Property inherent in Light.
Colours therefore are not connate with Natural Bodies, which are all of the same Hue in the dark. To this the Poet alludes, when he makes Darkness the Destruction of Colours[[140]].—Colours are only in the Rays of the Sun: In Natural Bodies is a Quality or Power to reflect the Light falling upon them, which striking the Eye, produces in the Spectator the Sensation of Colour.
[140]. Rebus nox abstulit atra colores.—Virgil.
Clouds often appear very beautifully coloured; they consist of aqueous Particles, between which Air is interspersed; therefore, according to the various Thickness of those aqueous Particles, the Cloud will be of a different Colour[[141]].
[141]. Boerhaave, Gravesand.
IX. AMPHISBÆNA Serpent, so called from αμφι & βαινω Biceps, a Monster with two Heads. This is a small and weak Creature, equal in Bulk to a little Finger, and about a Foot long, of a whitish or terraceous Colour; of the oviparous Family, of small Eyes, no otherways visible than the Prick of a little Needle; lives much under ground, and is often found by digging; feeds upon Ants. Under this Head, the Historian mentions three Serpents, viz.
The Brasilian, that has two Heads, and moves as a Crab[[142]].
[142]. Acosta.