Against this glorious path stands Perseus, sword upraised among its stars, while entangled in the fearful locks of the Gorgon Medusa glows Algol, the "Blinking Demon." This so-called demon-star actually winks, that is, it indulges in one long, slow wink at intervals of exactly 2 days, 20 hours and 49 minutes. Such a phenomenon used to be a source of terror to the Arabs who feared it might be predictive of some disaster. Although Perseus and the Gorgon are figments of fancy the wink of this amazing star is not imaginary by any means, for its light actually drops from the 2nd magnitude to the 4th magnitude and stays thus, half darkened, for about 20 minutes. Then it begins to slowly brighten and in the course of the next three hours regains its former brilliancy. In the clear air of the desert where the large stars burn like fire-brands, this change in brightness is very noticeable. Since it was not understood, it seemed terrifying and the superstitious Arabs imagined it to be the eye of a demon. It seemed a fitting star for the ancient Greeks to place on the grewsome head of the Gorgon Medusa where ever after it has flashed and faded in the most eerie fashion. The mystery of this winking star was not discovered until 1889. Then Vogel found that the periodical change of brightness in Algol is caused by a huge dimly lighted sun,--relatively dark compared with Algol,--which revolves around the major sun at a distance of only 3,000,000 miles. (The earth revolves at a distance of 93,000,000 miles from our sun.) Every time this darker body passes between Algol and the earth, five-sixths of the light from Algol is cut off, thus making it appear to blink. Vogel also found, through the aid of the spectroscope, the diameter and mass of these stars. Algol was found to be about one million miles in diameter with a mass less than half that of the sun while its companion was found to be about 800,000 miles in diameter with a mass about one fourth that of our sun. Thirty stars are now known to be of the Algol type. One of the most remarkable of these, V. Puppis, was found to be in the southern hemisphere and was carefully examined by Dr. A. W. Roberts. This star has a light variation of only 1½ days and is believed to whirl so closely to its companion that it is in actual contact.