explanation very easily. He pointed out that the bright body must be shining on the dark one, just as the Sun shines on our Earth and our Moon: it will illuminate half of it, and this half will be turned sometimes towards us and sometimes away from us, just as the Moon is sometimes full and sometimes new. This is seen easily enough in the case of the Moon, but in Algol we cannot see the two bodies separate from one another, we only see their combined light;

Fig. 35. nevertheless by these delicate observations we can say when one of them is full and when it is new just as easily as we can put the times of full Moon on the almanac. Is that not a wonderful result of patient work? And there is still more wonder to come. Mr. Stebbins found that he was able to calculate how large these two bodies were and how far apart (Fig. 36), and he found that the bright one must be 240 times as bright as our Sun, and even the fainter one, which has hitherto been called "dark," is 16 times as bright as our Sun! I think you will agree with me that this is a wonderful addition to our knowledge; we have been able to find out that a star which always appears just as a speck of light is really made up of two at a certain distance apart, one very bright and the other faint, partly shining of itself and partly being illuminated by the other; and that