'After a preliminary information in 1878 he presented the stroboscope invented by him in 1895 in its final form. The stroboscope disc, perforated in three rows (32, 16, 8) was electrified, had a siren for the adjustment of speed and vocal tone and a small telescope for magnified observation. Oertel observed the mechanism of the chest register and falsetto with this instrument and also examined the vibrations of the vocal folds in diseased conditions.'

'The first stroboscope developed for evaluating the larynx was a mechanical stroboscope where the light was interrupted by slits made in a rotating wheel (Oertel, 1895b). In this device, the constant light source is projected through a series of slits cut into a rotating wheel; the speed of the turning wheel could be adjusted. This would then cut the constant light source into a series of brief illuminations of the throat. The examiner used the head mirror to bounce the light source from the synchronstroboscope [sic] into the patient's oral cavity, off the laryngeal mirror, and shine the light to illuminate the vibrating vocal folds. By asking the patient to sustain a steady pitch phonation, the examiner could change the rate of the spinning wheel such that the vocal folds vibration and the rates of illumination of the vocal folds by each individual slit of illumination were equal or multiples of each other. This would then result in freezing of the vocal fold motion.' (3)

[NB: above copied from Google Books ed. Further commentary listed as appearing on p.7, but not accessible in preview version.]