EFFECTS OF REFRACTION. 
293 
of the refraction then must have been not much less 
than three degrees. 
In some other northern voyage it has been re¬ 
marked, that the sun was seen twenty minutes sooner, 
and as much later, than the regular time of sun-rising 
and setting. Mr. Bayly, who sailed as astronomer in 
the last voyage of Captain Cook, related to me, that 
when he was assistant astronomer to Maskelyne, cattle 
which fed in a meadow on the opposite side of the 
Thames were visible from Flamstead House at high 
water, and hid by the bank at low water. The effect 
of refraction in giving apparent altitude to distant 
objects which are in reality below the horizontal 
level, appears in all these cases to have been many 
degrees. 
As the water rose in the river, the objects on the 
farther side would be seen through a more dense 
medium, and the effect produced seems to have been 
giving apparently to the whole plain or surface be¬ 
yond the river, an inclination or increase of inclination 
towards the beholder; the distant parts being the 
most refracted, as must be the case in the plain 
of a glacis so rendered visible, which is to be ascribed 
to the more distant object being seen through a longer 
oxtent of atmosphere. From similar causes it may 
be imagined that the apparent horizon at sea will 
