Cited by O.F.F. Grünbaum, 'On Intermittent Stimulation of the Retina (Part I)', Journal of Physiology 21 (4-5) (1897), pp. 396-402.
Description:

'Alteration of luminosity without altering the nature of the source of light was easily accomplished by utilising a slight modification of a method suggested by Arago [note: 'Œuvres de Fr. Arago X. pp. 184-224. 1858.'], which depends upon the inclination of two Nicol's prisms. I compared this method of observation with that of the square of the distance of the source from the screen and found that the curves drawn as results of observations were similar.' (398)