sealing-wax which I have put there. The light which now goes to you from that piece of silver was obstructed by the edge of the basin, when there was no water there, and you were unable to see anything of it; but when we poured in water, the rays were attracted down by it, over the edge of the basin, and you were thus enabled to see the articles at the bottom.
I have shown you this experiment first, so that you might understand how glass attracts light, and might then see how other substances, like rock-salt and calcareous spar, mica, and other stones, would affect the light; and, if Dr. Tyndall will be good enough to let us use his light again, we will first of all show you how it may be bent by a piece of glass (fig. 19).
Fig. 19
[The electric lamp was again lit, and the beam of parallel rays of light, which it emitted, was
