18. It was suggested to them, whether they did not wish to make any use of their knowledges; for it is not enough to be delighted with knowledges, because knowledges have respect to uses, and uses ought to be their ends; that from knowledges alone no use results to themselves, but to others with whom they are willing to share or communicate them; and that it is not at all meet for a man who wants to become wise to stand still in knowledges alone, inasmuch as these are only instrumental causes, meant to be serviceable for the investigation of matters which ought to belong to the life. But they replied that they were delighted with knowledges, and that to them knowledges were uses. 19. Some of them, also, wish to appear, not as men, like the spirits of other earths, but as crystalline globes. Their wanting to appear so, although they do not, arises from the circumstance that the knowledges of immaterial things are in the other life represented by crystals. 20. The spirits of Mercury differ entirely from those of our Earth, for the spirits of our Earth concern themselves not so much about [immaterial] things as about worldly, corporeal, and terrestrial things, which are material. For this reason the spirits of Mercury cannot be together with the spirits of our Earth, and therefore wherever they meet them they flee away, for the spiritual spheres that are exhaled from both are almost contrary. The spirits of Mercury have a common saying, that they do not want to look at the sheath, but at things stripped of their sheath, thus at interior things. 21. There appeared a flame of considerable brightness, which blazed cheerfully, and this for about an hour. That flame signified the advent of some spirits of Mercury who, for penetration, thought, and speech, were prompter than those who preceded them. When they were come, they instantly ran over the things that were in my memory, but, owing to their promptness, I was unable to apperceive what they observed. Immediately afterwards, I heard them say that the matter was thus and thus. With regard to the things which I had seen in the heavens and in the world of spirits, they said that they knew them before. I perceived that a multitude of spirits who were consociated with them, was behind, a little to the left, in the plane of the occiput.