Book 3, Part 1, Question 20

[312] . . . Heat has a lot to do with fluidity, since it reduces the cohesiveness of bodies. It liquefies many bodies which are not otherwise fluids; and it increases the fluidity of thick fluids such as oil, resin, and honey, and thereby reduces their resistive force. However, it does not reduce the resistive force of water very much, which it would certainly have to do if a significant element of the resistance of water was due to the friction or cohesiveness of its parts. [313] Therefore the resistive force of water arises mainly from the inertial force of its matter.

Consequently, if all parts of celestial space were as dense as water, they would certainly have not much less resistive force than water. If they were as dense as mercury, they would have not much less resistive force than mercury. If they were completely and uniformly dense (i.e. full of matter, and with no empty spaces at all), however fluid and tenuous that matter was, it would have even greater resistive force than mercury. A completely solid sphere in a medium of this sort would lose more than half its motion while travelling a distance equal to three times its diameter. And a sphere which was not completely solid (such as the bodies of the planets), would come to a stop more quickly. So it is certainly necessary for the parts of space where the daily and regular motions of the planets and comets take place to be empty of all matter. The only possible exception will be various extremely tenuous vapours, exhalations, or effluences which rise from the atmospheres of the earth, planets, and comets.

The fictitious matter which is imagined as filling the whole of space is of no use for explaining the phenomena of Nature, since the motions of the planets and comets are better explained without it, by means of gravity; and it has never yet been explained how this matter accounts for gravity. The only thing which matter of this sort could do, would be to interfere with and slow down the motions of those large celestial bodies, and weaken the order of Nature; and in the microscopic pores of bodies, it would put a stop to the vibrations of their parts which their heat and all their active force consists in. Further, since matter of this sort is not only completely useless, but would actually interfere with the operations of Nature, and [314] weaken them, there is no solid reason why we should believe in any such matter at all. Consequently, it is to be utterly rejected.

But if this matter is rejected, we must reject with it the hypotheses according to which light is imagined to consist in a pressure or motion propagated through a medium of this sort. Precedents for rejecting such a medium are the very ancient and famous Greek and Phoenician philosophers who made empty space, atoms, and the gravity of atoms the principles of their philosophy, tacitly attributing the force of gravity to some cause distinct from matter. Modern physicists, in speculating about what things there were in Nature, could not account for this cause, and thought up false hypotheses in order to explain all phenomena without its help, and consigned its consideration to metaphysics. Whereas in fact the principal function and purpose of natural philosophy is to proceed by reasoning from effects to causes, until we finally arrive at the First Cause. We should not merely explain the mechanism of the universe, but in addition and above all we should eventually find answers to the following questions and others like them:

• What is there in the parts of space which are empty of matter?
  
  
• Why is it that the sun and the planets gravitate towards each other without any intervening matter?
  
  
• How is it that Nature does nothing in vain?
  
  
• What is the origin of the order and beauty of the universe?
  
  
• For what purpose were comets created?
  
  
• How is it that comets move in highly eccentric orbits, from and in every direction, and in all parts of the sky; whereas all the planets move through one and the same part of the sky, with the same alignment and in the same direction, in concentric orbits?
• What prevents the sun and the fixed stars from collapsing into each other?
  
  
• How is it [315] that the bodies of animals are constructed with such exquisite skill and wisdom, and for what purposes were their various parts intended?
  
  
• Could the eye have been constructed without knowledge of optics, or the ear without an understanding of sounds?
• How is it that the motions of the body obey the commands of the will?
  
  
• What is the origin of what is called ‘instinct’ in animals?
  
  
• Is not universal space the sensory of an incorporeal, living, and intelligent being, who discerns and comprehends innermost things themselves, and perceives them all from within and present in himself; whereas that in us which senses and thinks only looks at images of them in the brain? [n.1]

Certainly, even if every genuine advance made in this philosophy does not lead us immediately to knowledge of the First Cause, it is definitely the case that each advance perpetually brings us nearer and nearer to it, and is therefore to be considered as of the greatest significance. . . .

Book 3, Part 1, Question 24

[344] . . . Further, it seems to me that these fundamental particles not only have within themselves the force of inertia (together with the passive laws of motion which necessarily arise from this force), but also that they are perpetually receiving motion from certain active principles, such as gravity, and whatever causes fermentation and the cohesion of bodies. I do not consider these principles as ‘occult qualities’, which are imagined to arise from the ‘specific forms’ of things; but rather as universal laws [345] of nature, by which things themselves are formed. The phenomena of Nature show that such principles actually exist, even though it has not yet been explained what their causes are. It is meaningless to assert that the individual species of things are endowed with occult qualities, by virtue of which they have some sort of active power. Even if their causes were not yet known, it would still be a great scientific advance if two or three general principles of motion could be derived from the phenomena of Nature, and if it could then be explained how the properties and actions of all material objects followed from those principles. So I have no hesitation in asserting the existence of the principles of motion mentioned above, since they are to be found so widely throughout the whole of Nature.

Now, it seems that these principles were needed for compounding all material objects out of the hard and solid particles which I mentioned earlier, and that, in the original act of creation, they were combined and joined together by the will and wisdom of an intelligent agent. For it was appropriate that whoever created all things should have organised them and put them in proper order. If this is the true origin of things, it will be unworthy of a scientist to search for other explanations of the origin of the universe, or to imagine ways in which the whole universe could have arisen from chaos through the laws of Nature alone. Nevertheless, now that the universe has been formed, it can continue to exist for many generations by virtue of those laws. It is true that the comets move in highly eccentric orbits, from every direction and in every direction, in all parts of the heavens. However, there is no way that blind chance could have brought it about that all the planets move in concentric orbits with a similar motion. Admittedly there are some irregularities, [346] but they are scarcely worth noting, since they could be due to the mutual interaction of comets and planets. Besides, it is likely that, over a long period of time, they will eventually become so great that this structure of Nature will finally require a corrective hand. It must necessarily be accepted that such an amazing uniformity in the planetary system was brought about by intelligence and wisdom.

The same can be said of the uniformity there is in the bodies of animals. That is, virtually all animals have two sides, the right and the left, which are similar in form; and on each side, at the rear of their body, they have two legs, and at the front two arms, or legs, or wings attached to their shoulders; and between their shoulders they have a neck, with a head fixed onto it; and in the head there are two ears, two eyes, a nose, a mouth, and a tongue; and all these have similar positions in virtually all animals. Then there are all those other parts of the body which have been constructed with exquisite skill and wisdom — the eyes, the ears, the brain, the muscles, the glands, the heart, the lungs, the chest, the throat, arms, wings, swimming bladders, transparent membranes covering the eyes of some animals like spectacles, and other organs of sensation and motion, and the instincts of dumb animals and insects. Obviously the original uniformity of all these things cannot be attributed to anything other than the intelligence and wisdom of a powerful and immortal being — that is, who is present everywhere, and who can, by his will, move all bodies in his infinite sensory, and hence can fashion and re-fashion all parts of the whole universe as he chooses. It is analogous (though to a far higher degree) to the way in which our soul (which is the image of God within us) is capable of moving the parts of its body by its will.

Furthermore, space is infinitely divisible, but it is not necessarily the case that there is matter in every part of space. Consequently it must also be accepted that God is certainly able to create particles of matter with different shapes and sizes, which are also numerically and quantitatively distinct, because of the different proportions of empty space they contain. Perhaps he could even endow them with different densities and different powers. Because of this, he can vary the laws of Nature, and create worlds of different kinds in different parts of the whole of space. Certainly there is nothing in all this which is either self-contradictory, or contrary to reason.

It is as true in physics as it is in mathematics, that, in investigating difficult things, the method known as the ‘analytic’ method should always precede what is called the ‘synthetic’ method. The analytic method [n.2] is to collect observations, to attend to the phenomena, and thereby to derive simple things from compound things by reasoning — motive forces from motions, and generally, causes from effects, and general causes from particular causes, until one eventually arrives at the most general causes. The synthetic method is to take causes which have already been investigated and proved as one’s starting point, and use them to explain the phenomena which have arisen from them, and to prove those explanations.

In the first two books of this Optics, I used the analytic method to investigate and prove the innate differences between rays of light, as far as concerns their ability to be refracted or reflected, and their colour; and their alternations between being more easily reflected by bodies, or more easily passing through them; and the properties of bodies (both opaque and transparent) on which the reflections and colours of rays of light depend. Since these discoveries had been proved, they could be assumed as starting-points in the synthetic method, in order to explain the phenomena which flow from them. Further, I gave an example of this method at the end of Book I. [348] In this Book III, I only embarked upon the analysis of the things which still remain to be investigated about light and the effects it brings about in natural bodies. I touched many things only superficially, and, as I hinted, I left them to be investigated by others, and to be carried forward by the experiments and observations of those dedicated to research.

But if, by following this method, natural philosophy is at some time eventually completed in all its parts, and becomes a perfect system of knowledge, the scope of moral philosophy will simultaneously be extended. For in so far as natural philosophy enables us to understand what the First Cause of things is, what physical and moral power he has over us, and what benefits received are owed to him; to that extent, the Light of Nature will reveal to us our duty, both towards him, and towards each other. No doubt, if the worship of false gods had not blinded the minds of the heathens, their moral philosophy would have extended far further than the so-called four cardinal virtues. And those who taught the transmigration of souls, and the worship of the sun, the moon, and dead heroes, would instead have taught how our true and most beneficent Author should best be worshipped.

T H E   E N D

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