This doctrine of the relation of the various winds to the four elements and through them to the four humours is found in the _De Rerum Natura_ of Isidore of Seville, and is occasionally illustrated in European MSS. from the ninth century onward,[66] but we meet it set forth with special definiteness in the twelfth century in the translations from Messahalah. It is encountered also in the work of Herrade de Landsberg. In and after the thirteenth century it had become a commonplace. The description we have given of the universe was in the main set forth by Hildegard in her first work, the _Scivias_ (1141-50).[67] Subsequently she became dissatisfied with the account she had given, and while not withdrawing it, she sought in the _Liber Divinorum Operum_ (1163-70) so to modify the original presentment as to bring it more into line with accepted views. Thus she writes: ‘There appeared to me in vision a _disk_ very like that object which I saw twenty-eight years ago of the form of an _egg_, in the third vision of my book _Scivias_. In the outer part of the disk there was as it were the _lucidus ignis_, and beneath it the circle of the _ignis niger_ was portrayed ... and these two circles were so joined as to be one circle.’ There was thus one outer zone representing the fire. ‘Under the circle of the _ignis niger_ there was another circle in the likeness of the _purus aether_ which was of the same width as the two conjoined [outer] fiery circles. And below this circle again was the circle of the _aer aquosus_ as wide as the _lucidus ignis_. And below this circle was yet another circle, the _fortis et albus lucidusque aer_ ... the width whereof was as the width of the _ignis niger_, and these circles were joined to make one circle which was thus again of width equal to the outer two. Again, under this last circle yet another circle, the _aer tenuis_, was distinguishable, which could be seen to raise itself as a cloud, sometimes high and light, sometimes depressed and dark, and to diffuse itself as it were throughout the whole disk.... The outermost fiery circle perfuses the other circles with its fire, while the watery circle saturates them with its moisture, [cp. Wisdom of Solomon, xix. 18-20]. And from the extreme eastern part of the disk to the extreme west a line is stretched out [i.e. the equator] which separates the northern zones from the others’[68] (see Fig. 3 and Plates VII and VIII). [Illustration: Fig. 3. HILDEGARD’S SECOND SCHEME OF THE UNIVERSE Reconstructed from her measurements. AB, CD, and EF are all equal to each other, as are also GH, HK, and KL. The clouds are situated in the outer part of the _aer tenuis_, and form a prolongation downwards from the _aer aquosus_ towards the earth.]