4 Dr . Wollaston's Observations on horizontal Refraction ; 
appearance of all distant objects seen near the surface of the 
water was affected in a similar manner, but that scarcely any 
of them afforded images so perfectly distinct as the oblique line 
of an oar dipped in the water. 
A person present at the time (as well as some others to 
whom I have since related the circumstance) was inclined to 
attribute the appearance to reflection from the surface of the 
water; but, by a moderate share of attention, a very evident 
difference may be discovered between the inversion occasioned 
by reflection, and that which is caused by atmospherical refrac- 
tion. In cases of reflection, the angles between the object and 
image are sharp, the line of contact between them straight and 
well defined, but the lower part of the image indefinite and 
confused, by means of any slight undulation of the water. But, 
when the images are caused by refraction, the confines of the 
object and its inverted image are rounded and indistinct, and 
the lower edge of the image is terminated by a straight line at 
the surface of the water. In addition to these marks of diffe- 
rence, there is another circumstance which, if attended to, must 
at once remove all doubt; for, by bringing the line of sight 
near to the surface of the water, boats and other small objects 
are found to be completely hidden by an apparent horizon, 
which, in so short a distance, cannot be owing to any real cur- 
vature of the water, and can arise solely from the bending of the 
rays by refraction. 
When I reflected upon the causes which were probably in- 
strumental in the production of these phenomena, they appeared 
referrible to difference of temperature alone. After a succession 
of weather so hot that the thermometer, during one month 
preceding, had been 1 2 times above 8 o°, and on an average of 
