RECREATIVE SCIENCE. 



about in different pianos and angles, the course of the rays U 

 dearly defined, especially if a little smoke from a bit of brown 

 paper, dipped in a notation of nitre, and dried, U produced. The 

 moke aota like the clouds, vapours, and gases surrounding thn 

 earth, ami, by a secondary reflection, causes the rays of light to 

 .i.lo which might otherwise be too feeble to be appro- 



If the ray of light strikes in a perpendicular lino against the 

 mirror A B (Fig. 2), it simply returns again, and U reflected back 

 in a straight lino ; it is only (as shown above) when it falls ob- 

 liquely on the mirror that it is thrown off obliquely. There is 

 always a considerable loss of 

 light, even when the rays fall 

 perpendicularly on the reflect- 

 ing surface ; thus, supposing it 

 to be a very brilliant metal, 

 like quicksilver, 334 out of a 

 thousand are absorbed by the 

 metal and lost, and 666 only 

 reflected. When the incident 

 ray of light is at the smallest 

 angle, say 89|, like a cannon- 

 shot just grazing a surface, the 

 loss is less, and is represented 

 by 279, whilst 721 rays are re- 

 flected. Thus, more rays of 

 light are lost the nearer the in- 

 cident ray approaches the per- 

 pendicular. Only twenty-five 

 rays out of a thousand are re- 

 flected by plate-glass 

 at a perpendicular in- 

 cidence, and hence, 

 until the figure to be 

 reflected was illumi- 

 nated by the oxyhydro- 

 gen light, the illusion 

 called the " Ghost " Fig, 

 was not applied to the- 

 atrical or other pur- 

 poses of entertainment. 

 A model ghost appara- 

 tus is very easily con- 

 structed out of a box 

 (Fig. 3), with the lid off, 

 and turned on one side. 



Attached to the larger box, 

 on one side, as shown in the 

 ground-plan in Fig. 4, should 

 be a smaller one, containing 

 the lamp and lens, and figure 

 which is to be reflected in the 

 glass ; a simple contrivance, 

 snrh as a sliding door made of 

 tin, must be arranged, in order 

 to cut off the light or throw it 

 on, as the ghost is required to 



appear or disappear; the latter effects are caused by alternately 

 lighting up the figure and shading the light. 



In this model the box is represented by the letters A A A" A". 

 The glass, mode of common window-glass, is shown at B B, and 

 its angle and position should be carefully adjusted, so that the 

 reflection of the figure E should appear in the centre of the back 

 of the box at a ; the glass is masked in by scenery representing 

 the laboratory of an alchemist, and is shown at all the places 

 marked s. The figure is a small doll dressed to represent " a 

 woman in white," and is placed in a smaller box attached to 

 the side of the larger one, which is perforated with an aperture 

 to permit the figure to be reflected in the glass. To illuminate 

 the figure, an ordinary " bull's-eye," or a small magic lantern, 

 L, may be provided, the top of the little box being open to 

 allow the hot air from the chimney to escape, and in front of 

 the lamp, L, is the sliding panel of tin, D D, which controls the 

 light when the ghost is required to appear or disappear. The 

 proscenium is at A" A". In a plate of glass, both the anterior and 

 posterior sides reflect light, but more light is reflected from the 

 second than the first surface ; hence the thinner the glass the 

 better and clearer the reflection, which, with thick glass, is apt 



Pig. 4. 



to be hazy, in consequence of the two images being rsflsotod 

 together and overlapping eacii other. As light U reflected chiefly 

 from the second surface, more rays are thrown off by covering 

 the back with black Tarnish, or, better still, with an amalgam 

 of tin and mercury ; the intensity of the reflection of light from 

 the second surface then completely overpowers that of the first, 

 and, as in an ordinary looking-glass, it is the coated surface 

 which reflects the image. 



We see our faces in a looking-glass, because the f*c, being 

 strongly illuminated by natural or artificial light, emits rays, and 

 this reflected light moves towards the mirror A B (Fig. 5). 



To prevent the confusion 

 arising from the tracing oat of 

 too many rays, let one be 

 drawn from the forehead c I, 

 which, according to the laws of 

 reflection, will be sent to the 

 eye at o. Bat the mind pats 

 CEO into one line, and the 

 forehead is seen at H, as if the 

 lines CEO had turned on a 

 binge at E. Indeed, it seems 

 a wonderful faculty of the 

 mind to put the two oblique 

 lines c E and o E into one 

 straight line o H ; yet it is 

 seen every time we look into a 

 mirror, for the ray has really 

 travelled from c to c, and from 

 E to o, and it is that journey 

 that determines the 

 distance of the object; 

 and hence we see our- 

 selves as far beyond 

 the looking-glass sa 

 we stand from it As 

 the human eye is placed 

 in the highest part of 

 the body, the whole 

 person may be seen in 

 a looking-glass of but 

 half its length and 

 breadth, as in the 

 mirror a b. 



The rays from the 

 head travel to the 

 mirror in the line A a (Fig. 6), 

 perpendicularly to the mirror, 

 and are returned to the eye in 

 the same line, viz., a A ; conse- 

 quently, having travelled twice 

 the length A a, a man must see 

 his head at B ; rays from his 

 feet c, impinging on the bottom 

 of the mirror at b, will be re- 

 flected to the eye in the direc- 



tion b A. But seeing his feet 

 along the ray that approaches his eye last, he sees his feet at , 

 along the line A b D, and so of all the rest of his person. 



The angle of incidence being always equal to the angle of 

 reflection, it follows that a convex mirror \.e., a surface corre- 

 sponding with the outside of a watch-glasswill cause parallel 

 rays to become divergent, and it is easy to show that images 

 reflected by such a surface must be reduced apparently in size, 

 because so few of the reflected rays enter the eye. 



Suppose the arrow o b (Fig. 7) to be seen in a convex mirror, 

 c d, though rays proceed from the arrow in all directions, only 

 those reflected from the mirror in the space included in o 

 actually enter the eye, and if the mirror were removed the rays 

 a o and b n would meet at p ; but the reflected rays o r and * r 

 become more divergent, and do not meet at p, hence the angle 

 o rn being so much less than ap 6 (had the eye been at p), the 

 image t will be less than the object, and nearer the mirror. 



In the second and concluding portion of this paper on the 

 reflection of light, and the curious deceptions that are produced 

 by it, we shall endeavour to explain the special properties of 

 convex and concave mirrors, and the peculiar appearances; of 

 objects reflected in them. 



