'Yes,' she said, answering my look with a smile; 'it is a phial, made to hold an elixir more precious than itself. That silver vase is full of it; and now I am going to pour some into the phial. Then you will see something beautiful!' 'Is this that discovery you spoke of this afternoon?' 'Not the elixir; but the use to which we put it. The receipt for the elixir is a heritage from some of those old alchemists who used to carry on their experiments in this tower hundreds of years ago; and my father thinks it had been handed down to them from some philosopher far more ancient still. At all events he found the parchment on which the receipt was written in a concealed hollow of this wall--in that niche where the silver vase now stands. After long study, he succeeded in deciphering it; and then the elixir was made.' 'But what was it originally intended for--by the alchemists?' 'My father thinks it may have been their famous drink of Immortality,' replied Diana, taking the silver vase from its niche as she spoke. 'But he did not taste it, for he neither wished to live for ever nor to die by poison--and this may as well be an _aqua toffana_ as an _elixir vitæ_! But, while brewing it, he had noticed the strange effect of moonlight upon it; and as he was there searching for some means of strengthening the telescope, it occurred to him to try an experiment. And this was the result!' In saying these words, she slipped a funnel into the neck of the phial or lens, and, while I steadied the latter upon my knees, she poured into it about a pint of liquid from the vase. Then, taking it heedfully from my hands, she replaced it in its proper position in the neck of the telescope, secured it there by screwing on the ring, and finally, by turning a button attached to the pipe that supplied the lights, they were at once extinguished, and we were left in darkness. Yet no--not entirely so! For, when my eyes had had time to recover from the first impression of blackness, I began to perceive that there was still light in the room, though proceeding from a different quarter. It seemed to have a deep crimson hue; and in the course of a minute or two I could see it coming through the lens of the telescope, and evidently taking its colour from the liquid with which Diana had just filled it. But whence did this light originate? I must have asked this question aloud, for I heard Diana's voice answer:-- 'It is the light of the moon. Stoop down, now, and watch the elixir change. But be careful not to look through it, until I give you leave!' I stooped accordingly, and fixed my eyes upon the crystal. The sound of the mysterious music, rendered more weird by the darkness, did not prevent me from hearing the soft breathing of my companion, whose presence I felt close beside me, though I could not see her. She, too, was watching the changes of the magic liquid; and strange and beautiful in truth they were!