Scientific amusements . point of the line wesuppose radiating images of diffusion, which encroach oneach other. The clearest portions of these images ofdififusion mingle together and form distinct lines, whichshow multiplied images of the luminous line. Mostpersons will see two of these images : some, with the eyesin certain positions, will see five or six. To show clearly by experiment the connection existing between double images and radiated images from points,it is sufficient to make in a dark sheet ofpaper a small rectilinear slit, and at alittle distance from one end, on a linewith the s
Scientific amusements . point of the line wesuppose radiating images of diffusion, which encroach oneach other. The clearest portions of these images ofdififusion mingle together and form distinct lines, whichshow multiplied images of the luminous line. Mostpersons will see two of these images : some, with the eyesin certain positions, will see five or six. To show clearly by experiment the connection existing between double images and radiated images from points,it is sufficient to make in a dark sheet ofpaper a small rectilinear slit, and at alittle distance from one end, on a linewith the slit, a small round hole, as shownat a. Looking at it from a distance weshall see that the double images of theline have exactly the same distancebetween them that the niost brilliantparts of the starred figure of diffusionhave from the point, and that the latterare in a line with the first, as will be seen at b, where inthe image of diffusion of the luminous point, we only seethe clearest parts of star a of the 56 Vision. On lighted surfaces, to which the eye is not exactlyaccommodated, multiplied images are often remarkedthrough the passage from light to darkness being madeby two or three successive steps. A series of facts which have been collected under thetitle of irradiation, and which show that brightly-lightedsurfaces appear larger than they are in reality, and thatthe dark surfaces which surround them appear diminishedto a corresponding degree, explains this by the circum-stance that the luminous sensation is not proportional tothe intensity of the objective light. These phenomenaaffect very various appearances, according to the form ofrespective figures; they are generally seen with thegreatest ease and intensity when the eye is not exactlyaccommodated to the object examined, either by the eyebeing too near or too far off, or by using a concave orconvex lens, which prevents the object being seen is not completely wanting, even when theaccom
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Keywords: ., bookcentury1800, bookdecade189, booksubjectscientificrecreations
