The Theories of the Aether in the 17th Century

Modern research has shown how intimate is the connection between the different celestial bodies, proving a universal order.

Until the 17th century, the only influence known capable of passing from star to star was that of light.

• Newton added to this the force of gravity.
• It is now recognized that the power of communicating across vacuous regions is possessed also by the electric and magnetic attractions.

It is thus wrong to regard the heavenly bodies as isolated in vacant space.

• Around and between them is an incessant conveyance and transformation of energy.
• The ‘aether’ was the name given to the vehicle of this activity.

The aether is the solitary tenant of the universe, save for that infinitesimal fraction of space which is occupied by ordinary matter.

What is the relation between the medium which fills the interstellar void and the condensations of matter that are scattered throughout it?

The history of this problem may be traced back continuously to the early mid-17th century.

• It first emerged clearly in the reconstruction of ideas regarding the physical universe by René Descartes.

Descartes was born in 1596, the son of Joachim Descartes, Counsellor to the Parliament of Brittany.

As a young man, he worked in the military, and served in the campaigns of Maurice of Nassau, and the Emperor.

But at age 24, he had a profound mental crisis similar to those of many religious leaders. This led him to devote himself thenceforward to the study of philosophy.

The age which preceded the birth of Descartes, and that in which he lived, were marked by events which greatly altered the prevalent conceptions of the world:

• The discovery of America
• The circumnavigation of the globe by Drake
• The overthrow of the Ptolemaic system of astronomy
• The invention of the telescope

These helped to loosen the old foundations and to make plain the need for a new structure.

Descartes set himself to erect this.

His aim was the most ambitious that can be conceived – to create from the beginning a complete system of human knowledge.

The basis of such a system must necessarily be metaphysical. This part of Descartes’ work is that by which he is most widely known.

But his efforts were also largely devoted to the mechanical explanation of nature, which he regarded as one of the chief ends of Philosophy.[1]

The general character of his writings may be illustrated by a comparison with those of his most celebrated contemporary.[2]

Francis Bacon clearly defined the end to be sought for. He laid down how it was to be attained.

He recognized that to discover all the laws of nature was beyond the powers of one man or one generation. He left to posterity the work of filling in his framework.

Descartes, on the other hand, desired to leave as little as possible for his successors to do.

His was a theory of the universe, worked out as far as possible in every detail.

It is, however, impossible to derive such a theory inductively unless there is at hand sufficient observational data as basis.

• But it was not available in the age of Descartes

He was compelled to deduce phenomena from preconceived principles and causes, after the fashion of the older philosophers.

The errors that at last brought his scheme to ruin can be traced to the inherent weakness of his method

The contrast between the systems of Bacon and Descartes is similar to that between the Roman republic and the empire of Alexander.

• One is a career of aggrandizement pursued with patience for centuries
• The other is a growth of fungus-like rapidity, a speedy dissolution, and an immense influence long exerted by the disunited fragments.

The grandeur of Descartes’ plan, and the boldness of its execution, stimulated scientific thought to a degree before unparalleled.

• It was largely from its ruins that later philosophers constructed those more valid theories which have endured to our own time.

Descartes regarded the world as an immense machine, operating by the motion and pressure of matter.

“Give me matter and motion," he cried, “and I will construct the universe.”

A peculiarity which distinguished his system from that which afterwards sprang from its decay was the rejection of all forms of action at a distance.

He assumed that force cannot be communicated except by actual pressure or impact

• This compelled him to provide an explicit mechanism in order to account for each of the known forces of nature—a task evidently much more difficult than that which lies before those who are willing to admit action at a distance as an ultimate property of matter.

The sun interacts with the planets by sending them light and heat and influencing their motions.

• It followed from Descartes’ principle that interplanetary space must be a plenum, occupied by matter imperceptible to the touch but capable of serving as the vehicle of force and light.

This conclusion in turn determined the view which he adopted on the all-important question of the nature of matter.

Matter, in the Cartesian philosophy, is characterized not by impenetrability, or by any quality recognizable by the senses, but simply by extension. Extension constitutes matter, and matter constitutes space.

The basis of all things is a primitive, elementary, unique type of matter, boundless in extent and infinitely divisible.

In the process of evolution of the universe, 3 distinct forms of this matter have originated, corresponding respectively to:

1. The luminous matter of the sun
2. The transparent matter of interplanetary space
3. The dense, opaque matter of the earth.

“The first is constituted by what has been scraped off the other particles of matter when they were rounded; it moves with so much velocity that when it meets other bodies the force of its agitation causes it to be broken and divided by them into a heap of small particles that are of such a figure as to fill exactly all the holes and small interstices which they find around these bodies.

The next type includes most of the rest of matter; its particles are spherical, and are very small compared with the bodies we see on the earth; but nevertheless they have a finite magnitude, so that they can be divided into others yet smaller. There exists in addition a third type exemplified by some kinds of matter-namely, those which, on account of their size and figure, cannot be so easily moved as the preceding.

I will endeavor to show that all the bodies of the visible world are composed of these three forms of matter, as of three distinct elements; in fact, that the sun and the fixed stars are formed of the first of these elements, the interplanetary spaces of the second, and the earth, with the planets and comets, of the third.

For, seeing that the sun and the fixed stars emit light, the heavens transmit it, and the earth, the planets, and the comets reflect it, it appears to me that there is ground for using these three qualities of luminosity, transparence, and opacity, in order to distinguish the three elements of the visible world.[3]