The Light of Reason - Unpublished Selections Explained, Med. VIII.57

Meditation VIII.57 - The Light of Reason - Translated by George Long and rewritten by Russell McNeil

The sun appears to be poured down, and in all directions indeed it is diffused,¹ yet it is not effused.² For this diffusion is extension: Accordingly its rays are called Extensions because they are extended.³ But you may judge what kind of a thing a ray is, if you look at the sun's light passing through a narrow opening into a darkened room, for it is extended in a right line,⁴ and as it were is divided when it meets with any solid body which stands in the way and intercepts the air beyond;⁵ but there the light remains fixed and does not glide or fall off.⁶ Such then ought to be the out-pouring and diffusion of your understanding, and it should in no way be an effusion, but an extension, and it should make no violent or impetuous collision with the obstacles which are in its way;⁷ nor yet fall down, but be fixed and enlighten that which receives it. For a body will deprive itself of the illumination, if it does not admit it.⁸

Explanation

(1) Marcus's use of the word diffusion (diffused) is not referring here to the scattering of sunlight by the atmosphere which we now know does occur and explains for example why the sky is blue (short wavelengths - blues - are scattered much more than long wavelengths - reds). He refers here only to the rays of light from the sun that reach the surface of the earth. His use of the word diffusion implies that the rays that do reach the earth's surface arrive from different places on the sun's spherical surface but at differing angles because of the sun's shape and the individual ray's origin.

(2) The word effusion (effused) applies to the flow of a fluid or a gas through an opening. The gas or fluid spreads out in complex eddies. It does not proceed in a straight line through the opening. Light does not behave like this.

(3) In other words light travels in a straight line.

(4) A "right line" is a straight line.

(5) Marcus is not referring to a pinhole but a much larger opening. If he was referring to a pinhole he might have discovered the camera obscura or indeed the diffraction and interference of light - and hence inferred something about the wave nature of light. He is however coming tantalizingly close to such a discovery.

(6) Marcus is imagining a beam of the order of a searchlight being intercepted by a narrow pole or similar object. In this example the beam that is not intercepted by the pole will be split into two parts. The part of the beam that is intercepted by the pole illuminates the pole in the area that is intercepted. It does not effuse or splatter like a fluid.

(7) In other words our reasoning needs to follow a similar course. it ought to proceed toward its object and not be deflected by false opinion.

(8) Marcus is advocating an honest and determined and rigorous application of reason to the development of the understanding. There is no room in this process for compromise. Truth is truth. Unless we use our capacity for reasoning in a clear, enlightened and unbiased way, we will not develop the understanding we require to live according to nature.

Russell McNeil, PhD, is the author of The Meditations of Marcus Aurelius: Selections Annotated and Explained by Skylight Paths Publishing. The unpublished selections presented in this Blog are provided as supplemental material to the published selections which are annotated and explained in the book. The published selections are referenced in this Blog by page number and section.