ON ACCIDENTAL OR SUBJECTIVE COLORS, 217 



sists ill causing figures delineated on a disk to appear animated and alive. The 

 instrument with which this is effected is called a phantasmpe, and produces ap- 

 pearances truly singular. The same idea, since carried into execution in a 

 much moi'e imperfect manner, has given rise to the fhcnak'i stoscope. The latter 

 apparatus consists essentially of a disk of pasteboard perforated towards the 

 circumference with a series of narrow openings ; on the disk are painted small 

 figures which, when it is made to revolve opposite a mirror, seem, when the 

 image is observed through tbe openings, to become animated and to execute 

 different movements. The effect proceeds from such an arrangement of the in- 

 strument that figures which differ progressively from one another iu form, posi- 

 tion, or place, present themselves in quick succession to the eye, so that, the 

 persistence of the impressions connecting the images with each other, the same 

 figures appear to be passing in a continuous manner from one state to another. 

 [A very ingenious and interesting modification of this apparatus has lately 

 been invented by William Lincoln, a student of Brown University, Providence, 

 Rhode Island. In this the series of figures are drawn on long slips of paper, 

 one of which at a time is placed for exhibition around the interior circumference 

 of a hollow cylinder which is made to revolve on its axis iu a vertical position. 

 The figures are viewed through a series of narrow vertical slits in the cylinder, 

 and as these pass the eye in rapid succession, they give in each instance a 

 glimpse of the opposite figures, and thus produce the effect of apparent motion. 

 With this apparatus, which is called a zootrope, several persons can see the 

 effect at the same time. As the slits near the eye are moving in one direction, 

 while the figures on the opposite concave side of the cylinder are moving with 

 equal velocity in the opposite direction, the number of figures will appear to be 

 double. J. H.J 



Wo return now to subjective colors, still taking for our guide the excellent 

 dissertation of M. Plateau. 



SUBJECTIVE COLORS. 



First class — T?ie svccedancous colors. — If we regard attentively a colored 

 object placed on a black ground, keeping the eye constantly fixed on the same 

 point, Ave shall see, at the end of some moments, the color of that object grad- 

 ually lose something of its lustre ; and if the eyes be then suddenly directed to 

 a white surface, we shall presently see an image of the same form with the 

 object appear, but of a color complementary to the latter; the term comple- 

 mcntarij being understood to designate two colors which, added to or blended 

 with one another, produce white. Thus, the prolonged contemplation of a red, 

 object gives rise afterwards to a green image, and, conversely, the contemplation 

 of a green object is followed by the appearance of a red image ; if the object is 

 yellow or blue, the consequent object will be violet or orange, and vice versa. 

 Further, a tvJiite object produces in this way a blackish image, while a black 

 object produces a white image, lighter than the ground on which it is delineated. 

 All these images remain visible for some time ; their intensity, as well as dura- 

 tion, being so much greater as tlie time during which the object has been ob- 

 served is more considerable. These appearances form a portion of those to 

 which has been given the name of accidental colors, a name conferred by Buffon, 

 to whom, as Jurin asserts, we owe the first observations on this sort of phe- 

 nomena. Time, it will be seen, enters essentially into this first order of sub- 

 jective colors, since it is their nature to succeed to the objective colors which 

 cau.se them to appear. . 



properties of this first order of subjective colors. — The following are the 

 principal properties presented by these singular appearances : 



1. The disappearance of the images does not generally take place by a gradual 

 and continuous diminution of intensity ; they present, on the contrary, an alter- 

 nation of disappearances and reappearances ; occasionally the primitive impres- 



