On Vision. 3h 
eye that is incontrovertible. In short, these observations 
on my Theory, although they come in the borrowed dress 
of © candid philosophical discussion,” ate mere subterfuges 
opposed to mathematical demonstration. 
- Although the phenomenon of the rising moon has at- 
tracted the attention of men in all ages, yet a more extra- 
ordinary optical illusion, arising from the same cause, takes 
place when terrestrial objects are seen through a mist. Mr. 
Dunn, who has given a long dissertation on the phenome- 
non of the horizontal moon in the Philosophical Transac- 
tions, vol. Ixiv. observes, that ** mountains themselves, at 
a distance, sometimes appear larger than at other times. 
Cattle, houses, trees, all objects on the summit of a hill, 
when seen through a fog, and at a proper distance, appear 
enlarged. 
The following article is taken from the Ency. Brit, 
vol. xvii. p. 681. 
<< The writer of this article was passing the frith of Forth 
at Queensferry, near Edinburgh, one morning which was 
extremely foggy. Though the water be only two miles 
broad, the boat did not get within sight of the southern 
shore till it approached very near it. He then saw, to 
his great surprise, a large perpendicular rock, where he 
knew the shore was low and almost flat. As the boat ad- 
vanced a little nearer, the rock seemed to split perpendicu~ 
larly into portions, which separated at a little distance from 
one another. He next saw these perpendicular divisions 
move; and upon approaching a littie nearer, found it was 
a Sites of people standing on the beach, w vaiting the ar- 
rival of the ferry-boat.” 
The following extract of a letter, which now lies before 
me, is given as another instance of this property of vision. 
This letter I received soon after my papers on the Theory of 
the horizontal Moon were published in: the Philosophical 
Journal, from a gentleman on whose veracity I can ig 
the greatest confidence: 
* T beg leave (says this gentleman) to offer my testimony 
to that part of your first letter respecting terrestrial objects 
seen through 2 mist. When I was a young man, I was, 
like 
