(d) Picture a normal, within the bottle,

erected at the foot of the beam of light
as it enters: does the beam deviate
from the path outside the bottle to-
wards or away from the normal ?

(e) In a similar manner erect a normal at

the foot of the beam as it emerges on
the opposite side of the bottle: as
compared with its course through the
bottle, is the beam bent towards or
away from the normal?



268 NATURE STUDY FOB

Note. — Rays of light bent from their course by
passing from one transparent medium to another are
said to be refracted. Compare the direction of the
bending, with respect to the normal, when passing from
a rarer to a denser medium, with the direction when
passing from a denser to a rarer medium. For exam-
ple, from the air into the water, and from the water
into the air again, as in Experiment A.
(f) How the light strikes the surface of a

lens; are any rays normal to its surface?

(g) Judging from what was seen in the

experiment with the bottle, how the
lines of light must be refracted at the
incident surface of the lens. Remem-
ber that a normal to a curved surface
is a radius, or a radius extended, of the
sphere of which the surface is a part.
(h) How the rays must be refracted at the
'point of emergence.
(i) Whether the combined eflFect of the re-
fraction at the two surfaces is to cause
the rays to converge or to diverge.
(j ) From the fact that an image is formed,
what inference may be made as to the
relative direction of the enxergentrays.
