Albert Abraham Michelson

“ If the rotation of the earth does not entrain the æther, it is clear that one of the two pencils will be accelerated and the other retarded (relatively to the observing apparatus) by a quantity proportional to the velocity of the earth's surface, and to the length of the parallel of latitude at the place; so that a measurement of the difference of time required for the two pencils to traverse the circuit would furnish a quantitative test of the entrainement. ”

“ The system of interference-fringes should have its central or achromatic fringe bisected by the cross-hair if the æther rotates with the earth. If the æther does not partake of the earth's motion of rotation, the central fringe will be displaced from the cross-hair by the amount calculated from the formula. ”

“ The observation of interference-fringes produced by pencils which traversed a path 60 x 20 metres [5] presented so little difficulty, that it seems quite feasible to proceed to much greater distances. ”