The Goal of Yoga: Pentecost. Focus lecture for this evening's meeting of The Olive Branch, a Rudolf Steiner Study Circle

Ex Deo Nascimur        In Christo Morimur        Per Spiritum Sanctum Reviviscimus

Rudolf Steiner, Dornach, June 4, 1924:

When we consider how karma works we always have to bear in mind that the human ego, which is the essential being of man, the inmost being of man, has as it were three instruments through which it is able to live and express itself in the world. These are the physical body, the etheric body, and the astral body. Man really carries the physical, etheric, and astral bodies with him through the world, but he himself is not in any one of these bodies. In the truest sense he is the ego; and it is the ego which both suffers and creates karma.

Now the point is to gain an understanding of the relationship between man as the ego-being and these three instrumental forms — if I may call them so: the physical, etheric, and astral bodies. This will give us the foundation for an understanding of the essence of karma. We shall gain a fruitful point of view for the study of the physical, the etheric, and the astral in man in relation to karma if we consider the following.

The physical as we behold it in the mineral kingdom, the etheric as we find it working in the plant kingdom, and the astral as we find it working in the animal kingdom — all these are to be found in the environment of man here on Earth. In the cosmos surrounding the Earth we have that universe into which, if I may so describe it, the Earth extends on all sides. Man can feel a certain relationship between what takes place on the Earth and what takes place in the cosmic environment. But when we come to Spiritual Science we have to ask: Is this relationship really so commonplace as the present-day scientific conception of the world imagines? This modern scientific conception of the world examines the physical qualities of everything on the Earth, living and lifeless. It also investigates the stars, the Sun, the Moon, etc.; and it discovers — indeed it is particularly proud of the discovery — that these heavenly bodies are fundamentally of the same nature as the Earth.

Such a conception can only result from a form of knowledge which at no point comes to a real grasp of man himself — a knowledge which takes hold only of what is external to man. The moment, however, we really take hold of man as he stands within the Universe, we become able to discover the relationships between the several instrumental members of man's nature — the physical body, the etheric body, and the astral body — and the corresponding entities, the corresponding realities of being, in the Cosmos.

In regard to the etheric body of man, we find spread out in the Cosmos the universal Ether. The etheric body of man has a definite human shape, definite forms of movement within it, and so on. These, it is true, are different in the cosmic Ether. Nevertheless the cosmic Ether is fundamentally of like nature with what we find in the human etheric body. In the same way we can speak of a similarity between what is found in the human astral body and a certain astral principle that works through all things and all beings out in the far-spread Universe.

Here we come to something of extraordinary importance, something which in its true nature is quite foreign to the human being of today. Let us take our start from this. (A drawing is made on the blackboard). We have, first, the Earth; and on the Earth we have Man, with his etheric body. Then in the Earth's environment we have the cosmic Ether — the cosmic Ether which is of the same nature as the etheric in man. In man we also have the astral body. In the cosmic environment too there is Astrality. Where are we to find this cosmic Astrality? Where is it? It is indeed to be found, but we must first discover — what it is in the Cosmos that betrays the presence of cosmic Astrality; what it is that reveals it. Somewhere or other is the Astrality. Is this Astrality in the Cosmos quite invisible and imperceptible, or is it, after all, in some way perceptible to us?

In itself, of course, the Ether too is imperceptible for our physical senses. If I may put it so, when you are looking at a small fragment of Ether, you see nothing with your physical senses, you simply see through it. The Ether is like an empty nothingness to you. But when you regard the etheric environment as a totality, you behold the blue sky, of which we also say that it is not really there but that you are gazing into empty space. Now the reason why you see the blue of the sky is that you are actually perceiving the end of the Ether. Thus you behold the Ether as the blue of the heavens. The perception of the blue sky is really and truly a perception of the Ether. We may therefore say: In that we perceive the blue of the sky we are perceiving the universal Ether that surrounds us.

At first contact, we see through the Ether. It allows us to do so; and yet, it makes itself perceptible in the blue heavens. Hence the existence for human perception of the blue of the sky is expressed in that we say: The Ether itself, though imperceptible, yet rises to the level of perceptibility by reason of the great majesty with which it stands there in the Universe, revealing its presence, making itself known in the blue of the vast expanse.

Physical science theorizes materialistically about the blue of the sky; and for physical science it is indeed very difficult to reach any intelligent conclusion on this point, for the simple reason that it is bound to admit that where we see the blue of the sky there is nothing physical. Nevertheless men spin out the most elaborate theories to explain how the rays of light are reflected and refracted in a peculiar way so as to call forth this blue of the sky. In reality, it is here that the supersensible world begins already to hold sway. In the Cosmos the Supersensible does indeed become visible to us. We have only to discover where and how it becomes visible. The Ether becomes perceptible to us through the blue of the sky.

But now, somewhere there is also present the astral element of the Cosmos. In the blue sky the Ether peers through, as it were, into the realms of sense. Where then does the Astrality in the Cosmos peer through into the realms of perceptibility? The answer, my dear friends, is this.

Every star that we see glittering in the heavens is in reality a gate of entry for the Astral. Wherever the stars are twinkling and glittering in towards us, there glitters and shines the Astral. Look at the starry heavens in their manifold variety; in one part the stars are gathered into heaps and clusters, or in another they are scattered far apart. In all this wonderful configuration of radiant light, the invisible and super-sensible astral body of the Cosmos makes itself visible to us.

For this reason we must not consider the world of stars unspiritually. To look up to the world of stars and speak of worlds of burning gases is just as though — forgive the apparent absurdity of the comparison, but it is precisely true — it is just as though someone who loves you were gently stroking you, holding the fingers a little apart, and you were then to say that it feels like so many little ribbons being drawn across your cheek. It is no more untrue that little ribbons are laid across your cheek when someone strokes you, than that there exist up there in the heavens those material entities of which modern physics tells. It is the astral body of the Universe which is perpetually wielding its influences — like the gently stroking fingers — on the etheric organism of the Cosmos. The etheric Cosmos is organized for very long duration; it is for this reason that a star has its quality of fixity, representing a perpetual influence on the cosmic Ether by the astral Universe. It lasts far longer than the stroking of your cheek. But in the Cosmos things do last longer, for there we are dealing with gigantic measures. Thus in the starry heavens that we perceive, we actually behold an expression of the soul-life of the cosmic astral world.

In this way an immense, unfathomable life, yet, at the same time, a soul-life, a real and actual life of the soul, is brought into the Cosmos. Think how dead the Cosmos appears to us when we look into the far spaces and see nothing but burning gaseous bodies. Think how living it all becomes when we know that the stars are an expression of the love with which the astral Cosmos works upon the etheric Cosmos — for this is to express it with perfect truth. Think then of those mysterious processes when certain stars suddenly light up at certain times — processes which have only been explained to us by means of physical hypotheses that do not lead to any real understanding. Stars that were not there before, light up for a time, and disappear again. Thus in the Cosmos too there is a “stroking” of shorter duration. For it is true indeed that in epochs when divine beings desire to work in an especial way from the astral world into the etheric, we behold new stars light up and fade away again.

We ourselves in our own astral body have feelings of delight and comfort in the most varied ways. In like manner in the Cosmos, through the cosmic astral body, we have the varied configuration of the starry heavens. No wonder that an ancient science, instinctively clairvoyant, describes this third member of our human organism as the “astral” or “starry” body, seeing that it is of like nature with that which reveals itself to us in the stars.
It is only the Ego that we do not find revealed in the cosmic environment. Why is this? We shall find the reason if we consider how this human Ego manifests here on the Earth, in a world that is in reality threefold: physical, etheric, and astral. The Ego of man, as it appears within the Universe, is ever and again a repetition of former lives on Earth; and again and again it finds itself in the life between death and a new birth. But when we observe the Ego in its life between death and a new birth, we perceive that the Etheric which we have here in the cosmic environment of the Earth has no significance for the human Ego. The etheric body is laid aside soon after death. It is only the astral world, that shines in towards us through the stars, that has significance for the Ego in the life between death and a new birth. And in that world which glistens in towards us through the stars, in that world there live the beings of the higher hierarchies with whom man forms his karma between death and a new birth.

Indeed, when we follow this Ego in its successive evolutions through lives between birth and death and between death and a new birth, we cannot remain within the world of space at all. For two successive earthly lives cannot be within the same space. They cannot be within that Universe which is dependent on spatial co-existence. Here therefore we go right out of space and enter into time. This is actually so. We go out of space and come into the pure flow of time when we contemplate the Ego in its successive lives on Earth.

Now consider this, my dear friends. In space, time is still present, of course, but within this world of space we have no means of experiencing time in itself. We always have to experience time through space and spatial processes. For example, if you wish to experience time, you look at the clock, or, if you will, at the course of the Sun. What do you see? You see the various positions of the hands of the clock or of the Sun. You see something that is spatial. Through the fact that the positions of the hands or of the Sun are changed, through the fact that spatial things are present to you as changing, you gain some idea of time. But of time itself there is really nothing in this spatial perception. There are only varied spatial configurations, varied positions of the hands of the clock, varied positions of the Sun. You only experience time itself when you come into the sphere of the soul's experience. There you do really experience time, but there you also go out of space. There, time is a reality, but within the earthly world of space, time is no reality. What, then, must happen to us, if we would go out of the space in which we live between birth and death and enter into the spacelessness in which we live between death and a new birth? What must we do? The answer is this: We must die!
We must take these words in their exact and deep meaning. On Earth we experience time only through space — through points in space, through the positions of spatial things. On Earth we do not experience time in its reality at all. Once you grasp this, you will say: “Really to enter into time we must go out of space, we must put away all things spatial.” You can also express it in other words, for it is really nothing else than — to die. It means, in very deed and truth: to die.

Let us now turn our eyes to this cosmic world that encircles the Earth — this cosmic world to which we are akin both through our etheric body and also through our astral body — and let us look at the spiritual in this cosmic world. There have indeed been nations and human societies who have had regard only to the spiritual that is to be found within our earthly world of space. Such peoples were unable to have any thoughts about repeated lives on Earth. Thoughts about repeated lives on Earth were possessed only by those human beings and groups that were able to conceive time in its pure essence, time in its spaceless character. But if we consider this earthly world together with its cosmic environment, or, to put it briefly, all that we speak of as the Cosmos, the Universe; and if we behold the spiritual manifest in it, we are then apprehending something of which it can be said that it had to be present in order that we might enter into our existence as earthly human beings; it had to be there.

Unfathomable depths are really contained in this simple conception — that all that to which I have just referred had to exist in order that we as earthly human beings might enter this earthly life. Infinite depths are revealed when we really grasp the spiritual aspect of all that is thus put before us. If we conceive this Spiritual in its completeness as a self-contained whole, if we consider it in its own purity and essence, then we have a conception of what was called “God” by those peoples who limited their outlook to the world of space alone.

These peoples — at any rate in their wisdom-teachings — had come to feel: The Cosmos is woven through and through by a divine element that is at work in it, and we can distinguish from this divine element in the Cosmos that which is present, on the Earth in our immediate environment as the physical world. We can also distinguish that which, in this cosmic, divine-spiritual world reveals itself as the Etheric, namely that which gazes down upon us in the blue of the sky. We can distinguish as the Astral in this divine world that which gazes down upon us in the configuration of the starry heavens.

If we enter as fully as possible into the situation as we stand here, within the Universe, as human beings on this Earth, we shall say to ourselves: “We as human beings have a physical body: where, then, is the Physical in the Universe?” Here I am returning to something which I have already pointed out. The physical science of today expects to find everything which is on the Earth existing also in the Universe. But the physical organization itself is not to be found in the Universe at all. Man has in the first place his physical organization: then in addition he has the etheric and the astral. The Universe on the other hand begins with the Etheric. Out there in the Cosmos the Physical is nowhere to be found. The Physical exists only on the Earth, and it is but empty fancy and imagination to speak of anything physical in the far Universe. In the Universe there is the Etheric and the Astral.
There is also a third element within the Universe which we have yet to speak about in this present lecture, for the Cosmos too is threefold. But the threefoldness of the Cosmos, apart from the Earth, is different from the threefoldness of the Cosmos in which we include the Earth.

Let these feelings enter into our earthly consciousness: the perceiving of the Physical in our immediate earthly dwelling-place; the feeling of the Etheric, which is both on the Earth and in the Universe; the beholding of the Astral, glistening down to the Earth from the stars, and most intensely of all from the Sun-star. Then, when we consider all these things and place before our souls the majesty of this world-conception, we can well understand how in ancient times, when with the old instinctive clairvoyance men did not think so abstractly but were still able to feel the majesty of a great conception, they were led to realize: “A thought so majestic as this cannot be conceived perpetually in all its fullness. We must take hold of it at one special time, allowing it to work on the soul in its full, unfathomable glory. It will then work on in the inner depths of our human being, without being spoilt and corrupted by our surface consciousness.” — If we consider by what means the old instinctive clairvoyance gave expression to such a feeling, then out of all that combined to give truth to this thought in mankind in olden time there remains to us today the institution of the Christmas Festival.

On Christmas Night, man, as he stands here upon the Earth with his physical, his etheric, and his astral bodies, feels himself to be related to the threefold Cosmos, which appears to him in its Etheric nature, shining so majestically, and with the magic wonder of the night in the blue of the heavens; while face to face with him is the Astral of the Universe, in the stars that glitter in towards the Earth. As he realizes how the holiness of this cosmic environment is related to that which is on the Earth itself, he feels that he himself with his own Ego has been transplanted from the Cosmos into this world of Space. And now he may gaze upon the Christmas Mystery — the new-born Child, the Representative of Humanity on Earth, who, inasmuch as he is entering into childhood, is born into this world of Space. In the fullness and majesty of this Christmas thought, as he gazes on the Child that is born on Christmas Night, he exclaims: “Ex Deo Nascimur — I am born out of the Divine, the Divine that weaves and surges through the world of Space.”

When a man has felt this, when he has permeated himself through and through with it, then he may also recall what Anthroposophy has revealed to us about the meaning of the Earth. The Child on whom we are gazing is the outer sheath of That which is now born into Space. But whence is He born, that He might be brought to birth in the world of Space? According to what we have explained today, it can only be from Time. From out of Time the Child is born.

If we then follow out the life of this Child and His permeation by the Spirit of the Christ-Being, we come to realize that this Being, this Christ-Being, comes from the Sun. Then we shall look up to the Sun, and say to ourselves: “As I look up to the Sun, I must behold in the sunshine Time, which in the world of Space is hidden. Within the Sun is Time, and from out of the Time that weaves and works within the Sun, Christ came forth, came out into Space, on to the Earth.”

What have we then in Christ on Earth? In Christ on Earth we have That which coming from beyond Space, from outside of Space, unites with the Earth.

I want you to realize how our conception of the Universe changes, in comparison with the ordinary present-day conception when we really enter into all that has come before our souls this evening. There in the Universe we have the Sun, with all that there appears to us to be immediately connected with it — all that is contained in the blue of the heavens, in the world of the stars. At another point in the Universe we have the Earth with humanity. When we look up from the Earth to the Sun, we are at the same time looking into the flow of Time.

Now from this there follows something of great significance. Man only looks up to the Sun in the right way (even if it be but in his mind) when, as he gazes upwards, he forgets Space and considers Time alone. For in truth, the Sun does not only radiate light, it radiates Space itself, and when we are looking into the Sun we are looking out of Space into the world of Time. The Sun is the unique star that it is because when we gaze into the Sun we are looking out of Space. And from that world, outside of Space, Christ came to men. At the time when Christianity was founded by Christ on Earth, man had been all too long restricted to the mere Ex Deo Nascimur, he had become altogether bound up in it, he had become a Space-being pure and simple. The reason why it is so hard for us to understand the traditions of primeval epochs when we go back to them with the consciousness of present-day civilization is that they always had in mind Space, and not the world of Time. They regarded the world of Time only as an appendage of the world of Space.

Christ came to bring the element of Time again to men, and when the human heart, the human soul, the human spirit unite themselves with Christ, then man receives once more the stream of Time that flows from Eternity to Eternity. What else can we human beings do when we die, i.e. when we go out of the world of Space, than hold fast to Him who gives Time back to us again? At the Mystery of Golgotha man had become to so great an extent a being of Space that Time was lost to him. Christ brought Time back again to men.

If, then, in going forth from the world of Space, men would not die in their souls as well as in their bodies, they must die in Christ. We can still be human beings of Space, and say: Ex Deo Nascimur, and we can look to the Child who comes forth from Time into Space, that he may unite Christ with humanity. But since the Mystery of Golgotha we cannot conceive of death, the bound of our earthly life, without this thought: “We must die in Christ.” Otherwise we shall pay for our loss of Time with the loss of Christ Himself, and, banished from Him, remain held spellbound. We must fill ourselves with the Mystery of Golgotha. In addition to the Ex Deo Nascimur we must find the In Christo Morimur. We must bring forth the Easter thought in addition to the Christmas thought. Thus the Ex Deo Nascimur lets the Christmas thought appear before our souls, and in the In Christo Morimur the Easter thought.

We can now say: On the Earth man has his three bodies: the physical, the etheric, and the astral. The Etheric and Astral are also out there in the Cosmos, but the Physical is only to be found on the Earth. Out in the Cosmos there is no Physical. Thus we must say: On the Earth — physical, etheric, astral. In the Cosmos — no physical, but only the etheric and the astral.

Yet the Cosmos too is threefold, for what the Cosmos lacks at the lowest level, it adds above. In the Cosmos the Etheric is the lowest: on the Earth the Physical is the lowest. On Earth the Astral is the highest; in the Cosmos the highest is that of which man has today only the beginnings — that out of which his Spirit-Self will one day be woven. We may therefore say: In the Cosmos there is, as the third, the highest element, the Spirit-Selfhood [Manas].

Now we see the stars as expressions of something real. I compared their action to a gentle stroking. The Spirit-Selfhood that is behind them is indeed the Being that lovingly strokes — only in this case it is not a single Being but the whole world of the Hierarchies. I gaze upon a man and see his form; I look at his eyes and see them shining towards me; I hear his voice; it is the utterance of the human being. In the same way I gaze up into the far spaces of the world, I look upon the stars. They are the utterance of the Hierarchies — the living utterance of the Hierarchies, kindling astral feeling. I gaze into the blue depths of the firmament and perceive in it the outward revelation of the etheric body which is the lowest member of the whole world of the Hierarchies.

Now we may draw near to a still further realization. We look out into the far Cosmos which goes out beyond earthly reality, even as the Earth with its physical substance and forces goes down beneath cosmic reality. As in the Physical the Earth has a sub-cosmic element, so in Spirit-Selfhood the Cosmos has a super-earthly element.

Physical science speaks of a movement of the Sun; and it can do so, for within the spatial picture of the Cosmos which surrounds us we perceive by certain phenomena that the Sun is in movement. But that is only an image of the true Sun-movement — an image cast into Space. If we are speaking of the real Sun it is nonsense to say that the Sun moves in Space; for Space itself is being radiated out by the Sun. The Sun not only radiates light; the Sun creates Space itself. And the movement of the Sun is only a spatial movement within this created Space. Outside of Space it is a movement in Time, What seems apparent to us — namely, that the Sun is speeding on towards the constellation of Hercules — is only a spatial image of the Time-evolution of the Sun-Being.

To His intimate disciples Christ spoke these words: “Behold the life of the Earth; it is related to the life of the Cosmos. When you look out on the Earth and the surrounding Cosmos, it is the Father whose life permeates this Universe. The Father-God is the God of Space. But I make known to you that I have come to you from the Sun, from Time — Time that receives man only when he dies. I have brought you myself from out of Time. If you receive me, you receive Time, and you will not be held spellbound in Space. But you find the transition from the one trinity — Physical, Etheric, and Astral — to the other trinity, which leads from the Etheric and Astral to Spirit-Selfhood. Spirit-Selfhood is not to be found in the earthly world, just as the Earthly-Physical is not to be found in the Cosmos. But I bring you the message of it, for I am from the Sun.”

The Sun has indeed a threefold aspect. If one lives within the Sun and looks down from the Sun to the Earth, one beholds the Physical, Etheric, and Astral. One may also gaze on that which is within the Sun itself. Then one still sees the Physical so long as one remembers the Earth or gazes down towards the Earth. But if one looks away from the Earth one beholds on the other side the Spirit-Selfhood. Thus one swings backwards and forwards between the Physical and the nature of the Spirit-Self. Only the Etheric and Astral in between are permanent. As you look out into the great Universe, the Earthly vanishes away, and you have the Etheric, the Astral, and the Spirit-Selfhood. This is what you behold when you come into the Sun-Time between death and a new birth.

Let us now imagine first of all the inner mood of a man's soul to be such that he shuts himself up entirely within this Earth-existence. He can still feel the Divine, for out of the Divine he is born: Ex Deo Nascimur. Then let us imagine him no longer shutting himself up within the mere world of Space, but receiving the Christ who came from the world of Time into the world of Space, who brought Time itself into earthly Space. If a man does this, then in Death he will overcome Death. Ex Deo Nascimur. In Christo Morimur. But Christ Himself brings the message that when Space is overcome and one has learned to recognize the Sun as the creator of Space, when one feels oneself transplanted through Christ into the Sun, into the living Sun, then the earthly Physical vanishes and only the Etheric and the Astral are there. Now the Etheric comes to life, not as the blue of the sky, but as the lilac-red gleaming radiance of the Cosmos, and forth from the reddish light the stars no longer twinkle down upon us but gently touch us with their loving effluence.
If a man really enters into all this, he can have the experience of himself, standing here upon the Earth, the Physical put aside, but the Etheric still with him, streaming through and out of him in the lilac-reddish light. No longer now are the stars glimmering points of light; they are radiations of love like the caressing hand of a human being. As we feel all this — the divine within ourselves, the divine cosmic fire flaming forth from within us as the very being of man; ourselves within the Etheric world and experiencing the living expression of the Spirit in the Astral cosmic radiance — there bursts forth within us the inner awakening of the creative radiance of Spirit, which is man's high calling in the Universe.

When those to whom Christ revealed these things had let the revelation sink deep into their being, then the moment came when they experienced the working of this mighty concept, in the fiery tongues of Pentecost. At first they felt the falling away, the discarding of the earthly-Physical as death. But then the feeling came; This is not death, but in place of the Physical of the Earth, there now dawns upon us the Spirit-Selfhood of the Universe. “Per Spiritum Sanctum Reviviscimus.”

Thus may we regard the threefold nature of the one half of the year. We have the Christmas thought — Ex Deo Nascimur; the Easter thought — In Christo Morimur; and the Whitsun thought — Per Spiritum Sanctum Reviviscimus.

There remains the other half of the year. If we understand that too, there dawns on us the other aspect of our human life. If we understand the relationship of the physical to the soul of man and to the superphysical — which contains the true freedom of which man is to become a partaker on the Earth — then in the interconnection of the Christmas, Easter, and Whitsun festivals we understand the human freedom on Earth. As we understand man from out of these three thoughts — the Christmas thought, the Easter thought, and the Whitsun thought — and as we let this kindle in us the desire to understand the remaining portions of the year, there arises the other half of human life which I indicated when I said: “Gaze upon this human destiny; the Hierarchies appear behind it — the working and weaving of the Hierarchies.” It is wonderful to look truly into the destiny of a human being, for behind it stands the whole world of the Hierarchies.

It is indeed the language of the stars which sounds towards us from the thoughts of Christmas, Easter, and Whitsuntide; from the Christmas thought, inasmuch as the Earth is a star within the Universe; from the Easter thought, inasmuch as the most radiant of stars, the Sun, gives us his gifts of grace; and from the Whitsun thought, inasmuch as that which lies hidden beyond the stars lights into the soul, and lights forth again from the soul in the fiery tongues of Pentecost.

Enter into all this, my dear friends! I have told you of the Father, the Bearer of the Christmas thought, who sends the Son that through him the Easter thought may be fulfilled; I have told you further how the Son brings the message of the Spirit, so that in the thought of Whitsun man's life on Earth may be completed in its threefold being. Meditate this through, ponder it well; then for all the descriptive foundations I have already given you for an understanding of karma, you will gain a right foundation of inner feeling.

Try to let the Christmas, Easter, and Whitsun thoughts, in the way I have expressed them to you today, work deeply and truly into your human feeling, and when we meet again after the journey which I must undertake this Whitsuntide for the Course on Agriculture — when we come together again, bring this feeling with you, my dear friends. For this feeling should live on in you as the warm and fiery thought of Pentecost. Then we shall be able to go further in our study of karma; your power of understanding will be fertilized by what the Whitsun thought contains.

Just as once upon a time at the first Whitsun Festival something shone forth from each one of the disciples, so the thought of Pentecost should now become alive again for our anthroposophical understanding. Something must light up and shine forth from our souls. Therefore it is as a Whitsun feeling, to prepare you for the further continuation of our thoughts on karma, which are related to the other half of the year, that I have given you what I have said today about the inner connections of Christmas, Easter, and Whitsuntide.

Source: http://wn.rsarchive.org/Lectures/Dates/19240604p01.html#Xote01