4 
SOME NEW OPTICAL ILLUSIONS. 
of nearly uniform tint, and destitute of markings that would pro- 
duce upon the retina impressions like those of the adjacent objects. 
The railway affords many other instances of optical deception, 
and of these I will mention a few of which I am not aware that 
any specific notice has hitherto been taken. 
When a landscape is observed from a moving railway-train, all 
distant objects from the near hedgerows to the distant hills appear 
to be moving past in the opposite direction, the nearer objects 
having the greater apparent velocity. Consequently, if the atten- 
tion be fixed upon any object at some distance from the line, all 
objects beyond will relatively appear to be moving forward with 
the train, while objects nearer appear .to be moving backwards. 
The combined effect is to make the entire landscape appear to be 
revolving centrally round whatever point we fix out attention upon. 
Falling rain seen from a moving train always seems to fall 
obliquely (except in a very strong gale in the direction of the 
train’s motion) in a direction opposite to that of the motion of the 
train. But if another train happen to pass in an opposite direction, 
and we look out at this and follow it with our eyes, rain-drops 
falling between the two trains will seem to be flying forward with 
ourselves. 
If we stand on the platform of a station and watch a train 
approach, the end of the engine appears to enlarge or swell up 
as it approaches and occupies a larger area of the field of vision. 
Conversely the end of the last carriage of a retreating train 
appears to shrink down and contract as it diminishes in apparent 
magnitude. Stationary objects by the side of the line similarly 
appear to swell up as we approach them in a train, and to 
shrink together as we retreat from them. Curiously enough, this 
motion is also one which calls forth a certain ‘‘compensation ” 
in the action of the retina. For, suppose we have been watching 
objects enlarging as we approached them, and then suddenly 
transfer our gaze to the side of the carriage opposite to us, we 
