of aspect, our minds are subjected to countless phases of
thought, making the world around us constantly interesting, so it is
devised that we shall see the infinite wherever we turn, and marvel at
it, and delight in it, although perhaps in many cases unconsciously.

[Illustration: Fig. 4.]

[Illustration: Fig. 5.]

In perspective, as in geometry, we deal with parallels, squares,
triangles, cubes, circles, &c.; but in perspective the same figure takes
an endless variety of forms, whereas in geometry it has but one. Here
are three equal geometrical squares: they are all alike. Here are three
equal perspective squares, but all varied in form; and the same figure
changes in aspect as often as we view it from a different position.
A walk round the dining-room table will exemplify this.

It is in proving that, notwithstanding this difference of appearance,
the figures do represent the same form, that much of our work consists;
and for those who care to exercise their reasoning powers it becomes not
only a sure means of knowledge, but a study of the greatest interest.

Perspective is said to have been formed into a science about the
fifteenth century. Among the names mentioned by the unknown but pleasant
author of _The Practice of Perspective_, written by a Jesuit of Paris
in the eighteenth century, we find Albert Duerer, who has left us some
rules and principles in the fourth book of his _Geometry_; Jean Cousin,
who has an express treatise on the art wherein are many valuable things;
also Vignola, who altered the plans of St. Peter's left by Michelangelo;
Serlio, whose treatise is one of the best I have seen of these early
writers; Du Cerceau, Serigati, Solomon de Cause, Marolois, Vredemont;
Guidus Ubaldus, who first introduced foreshortening; the Sieur de
Vaulizard, the Sieur Dufarges, Joshua Kirby, for whose _Method of
Perspective made Easy_ (?) Hogarth drew the well-known frontispiece; and
lastly, the above-named _Practice of Perspective_ by a Jesuit of Paris,
which is very clear and excellent as far as it goes, and was the book
used by Sir Joshua Reynolds.[2] But nearly all these authors treat
chiefly of parallel perspective, which they do with clearness and
simplicity, and also mathematically, as shown in the short treatise
in Latin by Christian Wolff, but they scarcely touch upon the more
difficult problems of angular and oblique perspective. Of modern
books, those to which I am most indebted are the _Traite' P