On Refraction. 201 
poured in to the height of about one inch, the image floated at 
the surface. I now covered the tumbler up to this surface with 
black cloth, and desired an assistant to throw in different coins, 
while I kept my eyes shut, each of which I described on again 
opening my eyes, by looking at their images floating on the sur- 
face of the water an inch above the coins, my eye being ona line 
with that surface, as thus represented: ad a tumbler filled to the 
height of one inch with clear water, and covered with black 
cloth; ¢ a half-crown placed at the bottom; d the reflected 
image immediately over the coin, and seen by an eye at e. 
Now, sir, I would beg leave to ask any person, not entirely 
blinded by prejudice, Is there not a reflected image formed perpen- 
dicularly over the piece of money, capable of being seen by an eye 
above, below, and on a line with the surface ?- Query,—Does this 
reflected image send rays, or rather, an image, to the spectator’s 
eye? To see is to believe *. — But, sir, in your last Journal there 
is something about the analogy between reflection and refraction : 
however, as no particular objections are brought against my opi- 
nions, I must think it a waste of time to answer vague and angry 
generalities. I am weil aware, that my opinions on vision, light, 
and colours, are diametrically opposite to.those of the schools, 
and entertain too high a respect for their professors not to believe 
that they will undergo a liberal and unprejudiced examination. 
If the gentleman be really serious in denying the evidence of his 
. senses, he must come to particulars. 
Now let us examine this experiment according to the received 
laws laid down in every elementary treatise on optics; and I con- 
tend that no refraction or bending of the rays can possibly take 
place at d, for the rays cd enter the air perpendicular to the plane 
surface of the water; consequently they must pass on without 
any refraction. Mr. Harris has a figure (see fig. 8.) illustrating 
refraction at plane surfaces. Suppose the vessel empty, B K its 
side, and Q the object at the bottom; if the eye be at e, the ob- 
ject will be hid by the side BK; but by filling the vessel with 
water, it will become visible, and be seen at g. The ray QB 
being refracted into Be. Mr. Harris speaks as if an image were 
formed in the body of the water at g. For the purpose of making 
the rays of light euter the air in an oblique direction, mathema- 
ticians have made them to diverge from the point Q. On the 
contrary, we find by direct experiment, that an image of the 
half-crown is formed over the piece of money, which could not 
be the case were the rays diverged: that it is a reflected and not 
* If the rays cd are refracted in the direction e, the rays e should be re-~ 
fracted in the contrary direction dc; and an eyeunder the water at ¢ should 
perceive an object at e, which is impossible ; for then the sine of incidence 
would be equal to a radius. 
Vol. 59. No. 287. March 1822, Cc are- 
