ence of longitude to settle rival claims to the discovery of a new comet which has been picked up on the same night by different comet seekers. The discovery of Neptune more than seventy years ago is a classical instance of the amount of attention this priority question continues to excite. We need not, therefore, wonder that three centuries ago this discovery of sun-spots caused acute controversy, especially as Scheiner's explanation of the phenomenon was that already discarded by Galileo, namely, that the spots were really small planets revolving close to the sun. Other observers about the same time made the same discovery, and one of them, Fabricius, is generally accepted as the first to publish his observations, so that in modern times he is usually credited with priority. The idea of change or imperfection in the sun was exceedingly repugnant to accepted tradition. Scheiner was only permitted to publish his discovery anonymously, but nevertheless he was supported against Galileo by the Jesuits, as a body, and we may regard this as the actual beginning of Galileo's serious troubles.
About the same time Galileo had been drawing his own conclusions from observations of the moon. Having determined that the moon always turned the same face towards the earth, as easily proved by the configuration of its surface, he saw at once that the lunar day must be of the same length as the lunar month, and became convinced that no plants or animals could exist under such conditions.
A controversy on a totally different subject was the cause of the publication of Galileo's discourse on Floating Bodies in 1612. Aristotle had stated that the chief cause of a body floating was its shape, so that ice floated not because it was lighter than water, but because it was flat. Presumably neither Aristotle nor any of his followers had ever tried whether a ball of ice would sink. The
