In public gardens an apparently endless walk, under arches of gas-jets,
is often seen. But, on walking down it, it is seen to be of restricted
length, the illusion being obtained by an artful lessening of the sweep
and height of the arch, after, during a certain distance, the arches
have been regularly spaced out. This being done according to the rules
of perspective, the keenest are deceived.
[Illustration]