ABSTRACT
All physicists agree that the task of physics consists in tracing the phenomena of nature back to the simple laws of mechanics. But there is not the same agreement as to what these simple laws are. To most physicists they are simply Newton’s laws of motion. But in reality these latter laws only obtain their inner significance and their physical meaning through the tacit assumption that the forces of which they speak are of a simple nature and possess simple properties. But we have in this case no certainty as to what is simple and permissible, and what is not; it is just at this point that we no longer find any general agreement. Hence there arise actual differences of opinion as to whether or not this or that assumption is in accordance with the usual system of mechanics. It is in the treatment of new problems that we recognize the existence of such unanswered questions as a real hindrance to progress. So, for example, it is premature to attempt to base the equations of motion of the ether on the laws of mechanics until we have obtained perfect agreement as to what is understood by this name. 1
