IN January of the year 1610 Galileo, at Padua, in Italy, discovered four satellites revolving round Jupiter, and though more than 282 years elapsed in the interval, from that time to August, 1892, no additional satellites were detected near this planet, and astronomers naturally inferred that no others existed. The fact that Jupiter possessed four satellites has become familiar to every schoolboy, for it has been repeated in all the astronomical text-books published during nearly three centuries. Few people therefore could have imagined that the statement would ever be controverted or rendered untenable by new discoveries. In regard to the more distant planets Uranus and Neptune, there was every prospect of additional satellites being detected, but with Jupiter the circumstances were somewhat different. The four satellites were so bright and so palpably visible in very small telescopes that it was scarcely thought possible that another existed small enough to remain unseen. Moreover, there was a significant agreement in the relatively increasing numbers of the satellites surrounding the planets Mars, Jupiter, and Saturn. Mars was known to have two satellites, Jupiter four, and Saturn eight, the number doubling itself with each step outward from the sun, and it was considered probable that the harmony of the series would not be disturbed.