Without shadows, the forms of things would be unrevealed.
At different times of the day, objects will give shadows quite different in size and form, corresponding with the course of the sun. The difference of your own shadow exemplifies this, as well as the variation of the shadows in your room.
Direct your attention to the difference of the shadows thrown by candle-light; this luminary being smaller than the object placed against it, would make a figure, cut from a card, two or three inches high, give a shadow on the wall the size of life.
Place any object in the sun, and turn it round to the north, south, east, and west, at different periods; and, observing the difference of shapes in the shadows, will be found excellent practice.
Placed in certain directions, the form of every thing may be inferred from its shadow.
The shadow of a person arriving, on an open door, will, if the sun is behind him, distinguish to the inmate the comer's identity.
Shadow is most articulate and defined when the light is brightest, by reason of the contrast formed by the light; and will always, under these circumstances, appear much stronger than it is; though it is not so strong, in reality, as shadow in cloudy weather, from its being more equalized with the light. Shadow is only, more or less, by comparison with the brightness of the light. This is best explained by making a room dark by degrees, and holding up some object against the light as it diminishes, until it is quite dark.
The light of the sun always reflects a shadow equal to the object which it projects on a parallel plane. The sun being larger than the body illumined, throws a shadow less than that body. On the contrary, the light of a candle, being less than the object reflected, produces the contrary effect, the shadow increasing as it retires, not in parallels, but in rays, thrown by the light.
The figure and shape of a shadow is strictly defined by the form of the object producing it; as light occasions the existence of shadow. An excellent and well-turned remark is made by some writer on the subject, who says, 'It must be observed, that there are two points to be made use of: one of them, the foot of the light, which is always taken on the plane the object is placed upon; the other, the luminous body, the rule being common to the sun, torch, &c. with this difference, that the sun's shadow is projected in parallels, and that of the torch in rays, from the centre, as before mentioned. But as all objects on earth are so small in comparison of the sun, the diminution of their shadows is imperceptible to the eye, which sees them all equal, neither broader nor narrower than the object that forms them. On this account, all the shadows made by the sun are made in parallels.'
'To find the shadow of any object whatever opposed to the sun, a line must be drawn from the top of the luminary, perpendicular to the plane where the foot of the luminary is to be taken; and from this, an occult line, to be drawn through one of the angles of the plane of the object; and another, from the sun to the same angle. The intersection of the two lines will express how far the shadow is to go. All the other lines must be drawn parallel hereto.'