Stranica 24 [24]
OCR
CHAPTER I REFLEXIONS IN SMOOTH WATER E see objects by means of the light coming from them to the eye. They are either selfluminous, or, as more frequently happens, are visible by means of borrowed light; that is to say, they are illuminated by some external source, and from their surfaces a portion of the light they receive radiates in all directions. Light travels in straight lines unless some obstacle divert it from its course; and the passage of light in a straight line we call a ray.’ When a ray of light strikes a polished surface it is bent back or veflected, continuing its course in a new direction, and in order to understand the nature of “reflexions” in water we must be familiar with the law that every ray of light obeys when it falls upon such a surface. This law states that the angle of reflexion is equal to the angle of incidence; in other words, that the ray leaves the reflecting surface at an angle equal to that at which it falls upon it. For instance, if AB (Fig. 1) represent the surface of a plane mirror, a ray of light falling from a point P in the candle flame on to the mirror at C, will be reflected towards D, the angle PCB being equal to the angle " Ze., a beam of light of such minute transverse dimensions that it does not materially differ from a mere line.
