140

Logic 140

sequences independently of whether it is known or believed to be true or not; so that at the time it is selected as a test of the hypothesis we are either ignorant of whether it will support or refute the hypothesis ot at least do not select a test which we should not have selected if we had been so ignorant.
When Keppler had found that the elliptic orbit placed the planet Mars in the right longitudes he proceeded to test the hypothesis in two ways.
In the first place it had always been comparatively easy to find hypotheses approximately representing the longituses although not to the point of accuracy of Tyco Brake's observations.
But when these hypotheses were applied to the latitudes it had always been found that additional hypotheses of librations ot tiltings of the orbit of a complicated kind having little verisimilitude were required to come near to a representation of the latitudes.
Keppler