Arnold Sommerfeld

“ The deviation of both paths in unit time (OC in the first, OD in the second case) is small of second order, if are small of first order. The reason for this is, that in the first case the velocity from the moving system (ruler) is differently estimated than it is estimated from the stationary system (drawing plane) , because of the motion dependence of time; and correspondingly in the second case this applies to velocity . Exactly the same fact we have expressed above, that by execution of one space-time rotation in space xyl, the plane of the other space-time rotation will be displaced. ”

“ The single reason for this short paper was to show, that the deep space-time interpretation of Minkowski not only simplifies the general construction of the theory of relativity, but it is also reliable as a guidance concerning specific questions. ”

“ The sum of the angles in a spherical triangle is greater then two right angles, the sum of the angle of the sides in a right angled spherical triangle is thus greater then a right angle, as it is shown in Fig. ”