If after many preliminaries and prepa rations are made, a science gets stuck as soon as it approaches its end, or if in order to reach this end it must often go back and set out on a new path; or likewise if it proves impossible for the different co workers to achieve unanimity as to the way in which they should pursueh their common aim; then we may be sure that such a study is merely groping about, that it is still far from having entered upon the secure course of a science; and it is already a service to reason