Hence Kepler says very beautifully: Certum est vel in retinâ caussâ picturæ, vel in spiritibus caussâ impressionis, exsistere dilatationem lucidorum.
—Paralip. in Vitellionem, p. 220. Scherfer expresses a similar conjecture.{FOOTNOTE(class=seabeck)}Leonardo da Vinci observes that "a light object relieved on a dark ground appears magnified;" and again, " Objects seen at a distance appear out of proportion; this is because the light parts transmit their rays to the eye more powerfully than the dark. A woman's white head-dress once appeared to me much wider than her shoulders, owing to their being dressed in black."{FOOTNOTE(class=goethe)}Trattato della Pittura, Romas, 1817, p. 143-223. This edition, published from a Vatican MS., contains many obervations not included in the former editions.{FOOTNOTE} It is now generally admitted that the excitation produced by light is propagated on the retina a little beyond the outline of the image. Professor Plateau, of Ghent, has devoted a very interesting special memoir to the description and explanation of phenomena of this nature. See his 4 Memoire sur 1'Irradiation,' published in the 11th vol. of the Transactions of the Royal Academy of Sciences at Brussels."!{FOOTNOTE(class=goethe)}A few notes (marked with iverted cmmas and with teh signature S.F.) have been kindly furnished by a scientific friend.{FOOTNOTE}{FOOTNOTE}

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