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The Light Course
GA 320

Lecture V

27 December 1919, Stuttgart

My dear Friends,

Today I will begin by shewing, as well as may be with our limited resources, the experiment of which we spoke last time. You will remember: when an incandescent solid body spreads its light and we let this light go through a prism, we get a “spectrum”, a luminous picture, very like what we should get from the Sun, (compare Figure IVf), towards the end of Lecture IV). Now we can also obtain a luminous picture with the light that spreads from a glowing gas; however this picture only shews one or more single lines of light or little bands of light at different places, according to the substance used, (Figure IVg). The rest of the spectrum is stunted, so to speak. By very careful experiment, it is true, we should perceive that everything luminous gives a complete spectrum—expending all the way from red to violet, to say no more. Suppose for example we make a spectrum with glowing sodium gas: in the midst of a very feeble spectrum there is at one place a far more intense yellow line, making the rest seem even darker by contrast. Sodium is therefore often spoken of as giving only this yellow line.

And now we come to the remarkable fact, which, although not unknown before, was brought to light above all in 1859 by the famous experiment of Kirchhoff and Bunsen. If we arrange things so that the source of light generating the continuous spectrum and the one generating, say, the sodium line, can take effect as it were simultaneously, the sodium line will be found to act like an untransparent body. It gets in the way of the quality of light which would be appearing at this place (i.e. in the yellow) of the spectrum. It blots it out, so that we get a black line here in place of yellow, (Figure IVh). Simply to state the fact, this then is what we have to say: For the yellow of the spectrum, another yellow (the strength of which must be at least equal to the strength of light that is just being developed at this place of the spectrum) acts like an opaque body. As you will presently see, the elements we are compiling will pave the way to an understanding also of this phenomenon. In the first place however we must get hold of the pure facts.

We will now shew you, as well as we are able, that this dark line does really appear in the spectrum when we interpose the glowing sodium. We have not been able to arrange the experiment so as to project the spectrum on to a screen. Instead we will observe the spectrum by looking straight into it with our eyes. For it is possible to see the spectrum in this way too; it then appears displaced downward instead of upward, moreover the colours are reversed. We have already discussed, why it is that the colours appear in this way when we simply look through the prism.

By means of this apparatus, we here generate the cylinder of light; we let it go through here, and, looking into it, we see it thus refracted. (The experiment was shewn to everyone in turn).

To use the short remaining time—we shall now have to consider the relation of colours to what we call “bodies”. As a transition to this problem looking for the relations between the colours and what we commonly call “bodies”—I will however also shew the following experiment. You now see the complete spectrum projected on to the screen. Into the path of the cylinder of light I place a trough in which there is a little iodine dissolved in carbon disulphide. Note how the spectrum is changed. When I put into the path of the cylinder of light the solution of iodine in carbon disulphide, this light is extinguished. You see the spectrum clearly divided into two portions; the middle part is blotted out. You only see the violet on the one side, the reddish-yellow on the other. In that I cause the light to go through this solution—iodine in carbon disulphide—you see the complete spectrum divided into two portions; you only see the two poles on either hand.

It has grown late and I shall now only have time for a for a few matters of principle. Concerning the relation of the colours to the bodies we see around us (all of which are somehow coloured in the last resort), the point will be explained how it comes about that they appear coloured at all. How comes it in effect that the material bodies have this relation to the light? How do they, simply by dint of their material existence so to speak, develop such relation to the light that one body looks red, another blue, and so on. It is no doubt simplest to say: When colourless sunlight—according to the physicists, a gathering of all the colours—falls on a body that looks red, this is due to the body's swallowing all the other colours and only throwing back the red. With like simplicity we can explain why another body appears blue. It swallows the remaining colours and throws back the blue alone. We on the other hand have to eschew these speculative explanations and to approach the fact in question—namely the way we see what we call “coloured bodies”—by means of the pure facts. Fact upon fact in proper sequence will then at last enable us in time to “catch”—as it were, to close in upon—this very complex phenomenon.

The following will lead us on the way. Even in the 17th Century, we may remember, when alchemy was still pursued to some extent, they spoke of so-called “phosphores” or light-bearers. This is what they meant:—A Bologna cobbler, to take one example, was doing some alchemical experiments with a kind of Heavy Spar (Barytes). He made of it what was then called “Bologna stone”. When he exposed this to the light, a strange phenomenon occurred. After exposure the stone went on shining for a time, emitting a certain coloured light. The Bologna stone had acquired a relation to the light, which it expressed by being luminous still after exposure—after the light had been removed. Stones of this kind were then investigated in many ways and were called “phosphores”, If you come across the word “phosphor” or “phosphorus” in the literature of that time, you need not take it to mean what is called “Phosphorus” today; it refers to phosphorescent bodies of this kind—bearers of light, i.e. phos-phores.

However, even this phenomenon of after-luminescence—phosphor escence—is not the simplest. Another phenomenon is really the simple one. If you take ordinary paraffin oil and look through it towards a light, the oil appears slightly yellow. If on the other hand you place yourself so as to let the light pass through the oil while you look at it from behind, the oil will seem to be shining with a bluish light—only so long, however, as the light impinges on it. The same experiment can be made with a variety of other bodies. It is most interesting if you make a solution of plant green—chlorophyll (Figure Va). Look towards the light through the solution and it appears green. But if you take your stand to some extent behind it—if this (Figure Va) is the solution and this the light going through it, while you look from behind to where the light goes through—the chlorophyll shines back with a red or reddish light, just as the paraffin shone blue.

Figure 5a

There are many bodies with this property. They shine in a different way when, so to speak, they of themselves send the light back—when they have somehow come into relation to the light, changing it through their own nature—than when the light goes through them as through a transparent body. Look at the chlorophyll from behind: we see—so to speak—what the light has been doing in the chlorophyll; we see the mutual relation between the light and the chlorophyll. When in this way a body shines with one kind of light while illumined by another kind of light, we call the phenomenon Fluorescence. And, we may say: what in effect is Phosphorescence? It is a Fluorescence that lasts longer. For it is Fluorescence when the chlorophyll, for instance, shines with a reddish light so long as it is exposed to light. When there is Phosphorescence on the other hand, as with the Bologna stone, we can take the light away and the thing still goes on shining for a time. It thus retains the property of shining with a coloured light,—a property the chlorophyll does not retain. So you have two stages. The one is Fluorescence: we make a body coloured so long as we illumine it. The second is Phosphorescence: we cause a body to remain coloured still for a certain time after illumination. And now there is a third stage: the body, as an outcome of whatever it is that the light does with it, appears with a lasting colour. We have this sequence: Fluorescence, Phosphorescence, Colouredness-of-bodies.

Thus we have placed the phenomena, in a manner of speaking, side by side. What we must try to do is to approach the phenomena rightly with our thinking, our forming of ideas. There is another fundamental idea which you will need to get hold of today, for we shall afterwards want to relate it to all these other things. Please, once again, only think quite exactly of what I shall bring forward. Think as precisely as you can. I will remind you again (as once before in these lectures) of the formula for a velocity, say \(v\). A velocity is expressed, as you know, in dividing \(s\), the distance which the mobile object passes through, by the time \(t\). This therefore is the formula:


Now the opinion prevails that what is actually given in real Nature in such a case is the distance \(s\) the body passes through, and the time \(t\) it takes to do it. We are supposed to be dividing the real distance \(s\) by the real time \(t\), to get the velocity \(v\), which as a rule is not regarded as being quite so real but more as a kind of function, an outcome of the division sum. Thus the prevailing opinion. And yet in Nature it is not so. Of the three magnitudes—velocity, space and time,—velocity is the only one that has reality. What is really there in the world outside us is the velocity; the \(s\) and \(t\) we only get by splitting up the given totality, the \(v\), into two abstract entities. We only arrive at these on the basis of the velocity, which is really there. This then, to some extent, is our procedure. We see a so-called “body” flowing through space with a certain velocity. That it has this velocity, is the one real thing about it. But now we set to work and think. We no longer envisage the quick totality, the quickly moving body; instead, we think in terms of two abstractions. We dismember, what is really one, into two abstractions. Because there is a velocity, there is a distance moved through. This distance we envisage in the first place, and in the second place we envisage the time it takes to do it. From the velocity, the one thing actually there, we by our thinking process have sundered space and time; yet the space in question is not there at all save as an outcome of the velocity, nor for that matter is the time. The space and time, compared to this real thing which we denote as \(v\), are no realities at all, they are abstractions which we ourselves derive from the velocity. We shall not come to terms with outer reality, my dear Friends, till we are thoroughly clear on this point. We in our process of conception have first created this duality of space and time. The real thing we have outside us is the velocity and that alone; as to the “space” and “time”, we ourselves have first created them by virtue of the two abstractions into which—if you like to put it so—the velocity can fall apart for us.

From the velocity, in effect, we can separate ourselves, while from the space and time we cannot; they are within our perceiving,—in our perceiving activity. With space and time we are one. Much is implied in what I am now saying. With space and time we are one. Think of it well. We are not one with the velocity that is there outside us, but we are one with space and time. Nor should we, without more ado, ascribe to external bodies what we ourselves are one with; we should only use it to gain a proper idea of these external bodies. All we should say is that through space and time, with which we ourselves are very intimately united, we learn to know and understand the real velocity. We should not say “The body moves through such and such a distance”; we ought only to say: “The body has a velocity”. Nor should we say, “The body takes so much time to do it,” but once again only this: “The body has a velocity”. By means of space and time we only measure the velocity. The space and time are our own instruments. They are bound to us,—that is the essential thing. Here once again you see the sharp dividing line between what is generally called “subjective”—here, space and time—and the “objective” thing—here, the velocity. It will be good, my dear Friends, if you will bring this home to yourselves very clearly; the truth will then dawn upon you more and more: \(v\) is not merely the quotient of \(s\) and \(t\). Numerically, it is true, \(v\) is expressed by the quotient of \(s\) and \(t\). What I express by this number \(v\) is however a reality in its own right—a reality of which the essence is, to have velocity.

What I have here shewn you with regard to space and time—namely that they are inseparable from us and we ought not in thought to separate ourselves from them—is also true of another thing. But, my dear Friends (if I may say this in passing), people are still too much obsessed with the old Konigsberg habit, by which I mean, the Kantian idea. The “Konigsberg” habit must be got rid of, or else it might be thought that I myself have here been talking “Konigsberg”, as if to say “Space and Time are within us.” But that is not what I am saying. I say that in perceiving the reality outside us the—velocity—we make use of space and time for our perception. In effect, space and time are at once in us and outside us. The point is that we unite with space and time, while we do not unite with the velocity. The latter whizzes past us. This is quite different from the Kantian idea.

Now once again: what I have said of space and time is also true of something else. Even as we are united by space and time with the objective reality, while we first have to look for the velocity, so in like manner, we are in one and the same element with the so-called bodies whenever we behold them by means of light. We ought not to ascribe objectivity to light any more than to space and time. We swim in space and time just as the bodies swim in it with their velocities. So too we swim in the light, just as the bodies swim in the light. Light is an element common to us and the things outside us—the so-called bodies. You may imagine therefore: Say you have gradually filled the dark room with light, the space becomes filled with something—call it \(x\), if you will—something in which you are and in which the things outside you are. It is a common element in which both you, and that which is outside you, swim. But we have still to ask: How do we manage to swim in light? We obviously cannot swim in it with what we ordinarily call our body. We do however swirl in it with our etheric body. You will never understand what light is without going into these realities. We with our etheric body swim in the light (or, if you will, you may say, in the light-ether; the word does not matter in this connection). Once again therefore: With our etheric body we are swimming in the light.

Now in the course of these lectures we have seen how colours arise—and that in many ways—in and about the light itself. In the most manifold ways, colours arise in and about the light; so also they arise, or they subsist, in the so-called bodies. We see the ghostly, spectral colours so to speak,—those that arise and vanish within the light itself. For if I only cast a spectrum here it is indeed like seeing spectres; it hovers, fleeting, in space. Such colours therefore we behold, in and about the light.

In the light, I said just now, we swim with our etheric body. How then do we relate ourselves to the fleeting colours? We are in them with our astral body; it is none other than this. We are united with the colours with our astral body. You have no alternative, my dear Friends but to realise that when and wheresoever you see colours, with your astrality you are united with them. If you would reach any genuine knowledge you have no alternative, but must say to yourselves: The light remains invisible to us; we swim in it. Here it is as with space and time; we ought not to call them objective, for we ourselves are swimming in them. So too we should regard the light as an element common to us and to the things outside us; whilst in the colours we have to recognize something that can only make its appearance inasmuch as we through our astral body come into relation to what the light is doing there.

Assume now that in this space \(ABCD\) you have in some way brought about a phenomenon of colour—say, a spectrum. I mean now, a phenomenon that takes its course purely within the light. You must refer it to an astral relation to the light. But you may also have the phenomenon of colour in the form of a coloured surface. This therefore—from \(A\) to \(C,\) say—may be appearing to you as a coloured body, a red body for example. We say, then, \(AC\) is red. You look towards the surface of the body, and, to begin with, you will imagine rather crudely. Beneath the surface it is red, through and through. This time, you see, the case is different. Here too you have an astral relation; but from the astral relation you enter into with the colour in this instance you are separated by the bodily surface. Be sure you understand this rightly! In the one instance you see colours in the light—spectral colours. There you have astral relations of a direct kind; nothing is interposed between you and the colours. When on the other hand you see the colours of bodily objects, something is interposed between you and your astral body, and through this something you none the less entertain astral relations to what we call “bodily colours”. Please take these things to heart and think them through. For they are basic concepts—very important ones—which we shall need to elaborate. Only on these lines shall we achieve the necessary fundamental concepts for a truer Physics.

One more thing I would say in conclusion. What I am trying to present in these lectures is not what you can get from the first text-book you may purchase. Nor is it what you can get by reading Goethe's Theory of Colour. It is intended to be, what you will find in neither of the two, and what will help you make the spiritual link between them. We are not credulous believers in the Physics of today, nor need we be of Goethe. It was in 1832 that Goethe died. What we are seeking is not a Goetheanism of the year 1832 but one of 1919,—further evolved and developed. What I have said just now for instance—this of the astral relation—please think it through as thoroughly as you are able.