The invention is a frog panel assembly for a railway turn-out switch, as well as a rail intersection design and a frog casting therefor. The output of the optical cavity is a multiplicity of channels of data resulting from the differential absorption of light at various of the comb frequencies. A test pacing rate is selected from either the sensor-indicated rate or another rate. A bore seal is formed by milling a plurality of circumferential grooves, fed by a plurality of transverse holes intersecting the air passage. to prevent unintended withdrawal of the piston stopper.