il 
and on our Perception of Distance. 373 
When I simply looked sensationally on this scene, the lower fog 
line on the water seemed like a distant water horizon, and all 
above seemed but a cloudy sky. So strong was this impression, 
as not to be pomcapege impaired by seeing, half bums in the fo 
the sails of a rivers which looked as if resting in the cloug . 
sky. This ilncion Bt to lift the hill on which I stood, toa 
height greatly exceeding its actual elevation. The strong ‘like- 
ness of the fog boundary to a sea horizon rotated the apparent 
gee so as to make it dip much below the real one, towards 
the west; thus overcoming both my gravity sensibility and a 
Sumiling se gmk of the — 
A weeks since, in an early morning, when standing on 
the bow of a sail-boat in etuce harbor, 1 observed, during a 
thick fog, a singular apparent distortion of the water surface. 
The boat seemed to rest in a bowl or hollow of water, some four 
rods in radius. This bowl seemed bounded by a gently curved 
swell, which ran tangent to the apparent remote horizon. Thus 
the water around me seemed some four or five feet lower than 
the horizon water. This appearance I suppose to have resulted 
from the fog line along the water, looking like a dim distant hori- 
zon, and thus bringing the apparent limiting horizon circle muc 
too near. ‘This would make the apparent horizon dip below the 
true, and would thus give a false apparent level to the water as 
far in as to that point, where in looking down on it, the true level 
could be distinctly seen. The true and delusive levels seemed 
joined by a curved swell, the curve evidently depending on the 
height of the eye and the density of the fog. This observation, 
like the preceding, illustrates the power of our idea of a water 
horizon. 
5. If we look at the moon when a little above the horizon, its 
apparent enlargement may, by the simple act of shading with the 
hand all objects below the moon, be proved to be due in great 
part to the effect of — ee in magnifying our idea of 
its distance. The disc seems then to undergo a striking contrac- 
tion of size. On arene am hand, the moon seems again rapidly 
to enlarge. I think the effect of ‘this masking is to give an ap- 
be noticed too, that when we see the sun or moon in the horizon, 
through forest branches, especially when we are —_—- o a 
railroad car, they seem remarkably dilated. The great n 
of intervening branches and trunks is clearly the direct ious of 
this igre 
This reasoning applies directly to explaining the apparently 
ellipsoidal form of the sky dome. Seeing along the horizon 
many objects on which the binocular or perspective sensibility 
fastens to elaborate the sense of distance, the horizontal axis is 
