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culations to find Neptune, made the supposition that Bode's Law would go on in regular steps, and they too got led astray by this supposition. Suppositions are often made in such work, in order to simplify the calculations; but it would appear from these two cases far better to do without them if we can.

Fig. 54.

This discovery of Phœbe ultimately brought about an interesting situation. All the discoveries of satellites were at first made by other nations than England or America. Galileo started by finding four satellites of Jupiter, and it was not until nine in all had been discovered that anything was done in England. Once having started, however, England had the credit of seven out of the next eight, the other one falling to America. Then America continued with two satellites of Mars in 1877, a satellite of Jupiter in 1892, and Professor Pickering's