Abstract: The invention concerns a method and an arrangement for determining the position of a marker in an organic cavity, in particular for establishing local passage speeds within the framework of the medical diagnosis of the stomach-bowel tract. The object of the invention is to provide a solution which ensures position-determining accuracy of greater than 1 cm in all three co-ordinate directions and permits position-determining times of 10 seconds and less in each case. According to the invention, this object is achieved in that at least one coil is acted upon in a time interval in a pulsed manner by current whose sign changes in each case between two current pulses, when the primary magnetic field, of the coil, produced thereby has died out to sufficiently low values. The secondary magnetic field generated by a marker is measured separately at least once by anisotropic magnetic field sensors parallel and perpendicular to the coil axis.

Abstract: In a Faraday microscope for examining specimens with stray magnetic fields in a reflected light beam path with a magnetic indicator film arranged in front of the specimen, the influence of the specimen on the indicator film is evaluated with the indicator film arranged as the termination of the microscope objective, the indicator film advantageously being arranged on an optically transparent substrate. The indicator film and substrate are taken into account in the optical calculation of the microscope objective.