Page:A Voyage in Space (1913).djvu/36

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"fore"-sight at the further end of a straight bar pointed towards the star. Compared with what we can now do with a telescope the observations were rough indeed; and yet they were the means by which we learnt the laws of Gravity. This, however, was not until many years after Tycho Brahe himself was dead: he made thousands of observations, but

Voyage in Space page016.png

A Sextant used by Tycho Brahe.

did not live to find out all they could tell him. Fortunately he had a devoted pupil, Kepler, a German, who went on working at them, and found out the very important things they showed. Kepler is represented with a pair of compasses in his hand, showing that he was fond of measuring things, which is really the chief business of an astronomer—not merely looking at the stars and planets, but measuring their distances apart, or something else that can be measured. Tycho Brahe was also animated by this devotion to measurement, otherwise Kepler would not have been able to use his work as he did. By use of it he found three great laws of movement for the planets. No one suspected the simple laws of Gravity as yet, but Kepler made it possible to find them by establishing the three great laws of movement which have ever since been called by his name