But the greatest marvel of Perseus is the “Demon Star,” Algol, in the head of Medusa, which is represented depending from the hero’s right hand. Algol bears the Greek letter Beta (β). It is the most wonderful of variables, and its variations can be watched without any instrumental assistance. For the greater part of the time it is of nearly the second magnitude; but once every two days, twenty hours, and forty-nine seconds it begins suddenly to lose light, and in about four hours or less it fades to nearly the fourth magnitude, being then no brighter than some of the faint stars around it. Almost immediately it begins to brighten again, and in the course of about three hours is seen shining with its pristine splendor. The cause of these singular variations is believed to be the existence of a dark star, or a mass of meteors, revolving round Algol at such close quarters that a distance of only 3,000,000 miles separates the centres of the two. Algol itself is demonstrably considerably larger than our sun, but of less density. The Arabic name for this star was _Al Ghul_, the “Demon,” or “Fiend of the Woods,” and our word ghoul comes from it. The imagination of a Poe could not have represented a more startling thing--a sun that winks like a gloating demon! One may easily cultivate an uncanny feeling while watching it. No one need be surprised that the astrologers make much of the malign influence of Algol. If one had faith in them, one might as well be born with the millstone of fate tied to his neck as to have Algol in his nativity. Below Perseus, and not very high above the horizon, sparkles the brilliant Capella, but that is for the next chapter. We turn to Cassiopeia. Her “W,” or “Laconian Key,” is a familiar asterism to all who know anything at all of the starry heavens. The five stars forming this figure are also represented as marking the Chair in which the unfortunate though beautiful queen sits. There is a delightful reference to this “Chair” in Xavier de Maistre’s _Expédition Nocturne autour de ma Chambre_. When the hero discovers the slipper of his fair neighbor of the upper flat visible on the balcony above, he wishes “to compare the pleasure that a modest man may feel in contemplating a lady’s slipper with that imparted by the contemplation of the stars.” Accordingly, he chooses the first constellation that he can see. “It was, if I mistake not, Cassiopeia’s Chair which I saw over my head, and I looked by turns at the constellation and the slipper, the slipper and the constellation. I perceived then that these two sensations were of a totally different nature; the one was in my head, while the other seemed to me to have its seat in the region of the heart.”