Image Position Measurement by Polarimetry

The problem of measurement of the position of a small image is shown to be equivalent to the measurement of a path-difference. As this can be done with great precision, the measurement of position should also be susceptible of great accuracy. A practical method of doing this is outlined and an experimental check of the process described. This enabled the measurement to be made to 1/900 of the conventionally defined resolving power. The conditions to be satisfied in order that the method should work satisfactorily are derived. Some applications in astronomy are outlined, with rough estimates of the results to be expected.