On Refraction. 249 
which cannot be accomplished at once on the potter’s wheel. 
One man and a boy are capable of making from ten to twelve 
hundred per day. The principle is peculiarly adapted for the 
formation of a number of chemical apparatus, muffles, retorts, 
tubes, &c. 
LIV. On Refraction. By J. Reape, M.D. 
To Dr. Tilloch. 
Sir, — A VERY common experiment, no less interesting than 
surprising, is shown in lecture-rooms for the purpose of illustrating 
the theory of refraction. A piece of money is placed at the bot- 
tom of an empty basin, the experimenter retiring until the edge 
intercepts the object: an assistant then pours in water; the piece 
of money seems to rise over the edge, becoming perfectly visible 
and well defined. This experiment seldom fails to surprise the 
audience, handed down from one generation to another, even 
from the days of Aristotle; yet J am led to believe the real cause 
is little understood. Mr. Harris gives the following explanation 
in his Optics, page 25: 
“* Hence (says this writer) we have the common phenomenon 
of a shilling or other object placed in an empty vessel, appearing 
to be elevated higher and higher as the 
vessel is filled with water. Suppose the 
vessel empty, B K its side, and Q the 
object at the bottom; if the eye be at 
c, the object will be hid by the side B 
K, but by filling the vessel it will be- 
come visible and be seen at G; the 
ray QB being refracted or bent into 
Bc; and if the eye be so placed as to 
see the object at Q when the vessel was |. 
empty; while it is filling the object will appear to rise gradually 
in the line QG. Hence the piece of money appears one quar- 
ter nearer the eye than it really is: and on the same principle a 
river is one quarter deeper than it appears. QA: GA::4:3.” 
Independently of those experiments, there are insurmountable 
objections to this reasoning. How can any bending of the rays 
of light bring the object nearer to the eye? If we bend a piece of 
iron wire, we certainly shorten the length it extended ; but if the 
rays of light were so bent, they would fall short of the object : 
besides, if the rays were bent at B, on passing from water into 
air, a tube bent in the same direction should enable us to see the 
object ; which is never the case. However, it is unnecessary to 
bring forward more objections than the following experiment. 
Vol. 58, No. 282. Oct, 1821. li Exp- 
