Page:A Voyage in Space (1913).djvu/69

Rh about the distance of the Moon on my simple word; I want you to know for yourselves how it is measured. We saw what an advantage it was to Galileo to try things for himself rather than take them on trust; and though we cannot exactly measure the Moon's distance in this room, we can imitate the method with something else. We cannot perhaps make so good an imitation as we did of Galileo's experiment, by dropping balls from the roof, but we will make as good an imitation as we can. When astronomers measure the distance of the Moon or of any other object in the sky, they use precisely the same method as surveyors use on Earth, and indeed the method which every one of us uses nearly every moment of our wakeful lives. With our two eyes we are continually trying to estimate how far away men and things are from us. At this moment, for instance, I am trying to see whether the important people are in the front rows and the unimportant people at the back; and I do it really by squinting. I turn inwards my two eyes to converge on some one in the front row, and I can feel how much squint it takes: then I converge them similarly on some one in the back row and I feel that it does not take so much. This process is quite unconscious because we have all done it so many millions of times that we do it without thinking, but our muscles and nerves tell us the result just as well. From what they tell me I conclude that the people are pretty much in their right places.

Not only is this measurement of distance with our