'The question whether "white-black value" alone or "colour-brightness value" with " white-black value" (Hering) has to be reckoned with in flicker-photometry, has been recently treated by Schenk [note: Pflüger's Archiv, LXIV. p. 607. 1896.']. In connection with that interesting work it is noteworthy that the replacement of yellow (chrome) in disc (figure 1) by white (chinese) does not appreciably increase the difference in flicker between the two ring-bands.' (43)