of EZ, leaving only FZ for all distances greater than 2; 3 uses up still more, leaving only GZ: and yet we have a great many still to come, 4, 5, 6, up to hundreds and millions. All these have to be crowded into an arc which gets continually smaller and smaller, so that we find it more and more difficult to make the marks or to distinguish between them. When you get home, take a card and mark it for
CARD OF "SQUINT"
Fig. 10.
yourself and see how many "squints" you can put accurately upon it. You may get up to 10, or 20 even; but you will soon find how difficult it becomes. Probably you have a watch with the 60 minute spaces marked. Well, one minute space is the "squint" mark for 10: divide it into halves and you get the "squint" mark for 20. One half must have all the marks between 10 and 20, the other must have everything above 20! When we use our eyes we have no card, but we attend to the feelings of our nerves and muscles, which can scarcely distinguish between these various "squints" at long distances. That is why it is harder to put the match to the end of a very long cigar than of a short one.
And when the astronomer tries to determine distances of objects in the sky, such as the Moon, he
