when I told him that it was in order to show his town to my friends
at home in my own country, and to let them see how extensive it was.
He took much interest in my operations, and conducted me to a
spot whence I could have the best prospect.
His choice was just, and I made -my drawing from the very
point of view to which he brought m e; but the numerous clusters
of dwellings spread so far both to the right and to the left, that the
laws of perspective would not allow me to include in my sketch
more than a third of the town, without having recourse to the principle
of a cylindric medium. * But as there was no variation in the
» The method of drawing in perspective on the principle of an imaginary cylindric
medium not having hitherto, I believe, been noticed by any writer on this branch of optics,
it becomes necessary to make the above allusion to it intelligible by a brief explanation. —
The usual method supposes this medium to be a transparent plane through which
the objects are beheld; the ‘ point of sight,’ to be that point in the plane, where a line
from the eye, or visual ray, would strike it perpendicularly; the ‘ point of distance,’ to be
a point in the plane, at a distance from the point of sight, equal to that between the eye and
the medium; and S accidental points’ to be those to which all lines not actually parallel to
the medium, nor perpendicular to it, appeal- perspectively to converge. This, at least, is the
method usually taught, and is that which I acquired under the instruction of that excellent
artist Mr. Nattes', whose works prove that he was truly a master in the art of perspective
drawing. In putting this method into practice, the view seen through the medium, or
rather the medium itself on which the objects are imagined as depicted, becomes the
picture; which picture, to be strictly and optically correct, must represent these objects
larger in proportion as their places on the medium may be farther from the point of sight;
an enlargement similar to that which is required in the projection of extensive maps.
Until the extent of landscape exceed an angle of about fifty degrees, this enlargement
will be inconsiderable in drawings of moderate size; but when it is much beyond
that, the picture, if the correct principles of perspective be strictly adhered to, must become
an anamorphosis, and will not admit of being viewed in any other position, than
that in which the eye of the spectator is exactly opposite to the ‘ point of sight,’ and at
the same distance from it, as the ‘ point of distance.’ This is, however, the position in
which all perspectives ought to be viewed; notwithstanding a practice, too often seen in
galleries, of hanging such pictures so that the visual ray cannot fell perpendicularly upon
its proper point, nor even upon any part of the painting. .
But by adopting that principle which supposes this medium to be the superficial concavity
of a perpendicular cylinder, the eye being placed at any point in the axis, a method
is found by which a landscape may be extended to any number of degrees, and by which
every object on the same horizontal line may be delineated in the same proportion; which
may be demonstrated geometrically by showing that all the visual rays from the axis of a
cylinder, and falling on the same horizontal line, are equal; while all those which fell upon
a olane, increase in . length as they spread farther from the point of sight. In practice,
appearance of the different clusters, nor in that of the houses, a view
of one-third would convey a complete and just idea of the whole.
The Chief and his party seated themselves around me, and
watched my proceedings, not with that degree of curiosity which
indicated a desire of learning the art, but merely with that which
the novelty of the affair excited. Some, without much reflection,
indeed, took their stand before me, and on my requesting them to
move aside, Mattlvi scolded them very unceremoniously, for obstructing
my view : on which they laid themselves down on the rocks,
or stationed themselves behind me.
The Chief's dinner-hour happened during my drawing; and, as
he chose to remain with me till I had finished my work, his servants
brought his dinner to him. He used most frequently, or when not
the cylindric method has several advantages and facilities, although it requires that very
long horizontal right lines which are much above or below the ' horizontal line’ properly
so called, or that which passes through the point of sight, should be represented more or
less curved; but this is a case which very rarely occurs. In landscape-pictures which
comprehend a larger horizontal angle than the eye can clearly take in at one yiew, such as
the cylindric principle admits of, it would be incorrect to enlarge the angle of altitude, or
height of the picture, in the same proportion; although this precept, which naturally
depends on the powers of vision, appears to be in general little attended to.
In the course of studying this art from nature, we may discover that all the rules
which are usually given us for delineating the different parts of a view where a great
number of ‘ accidental points’ are required, may be reduced to one, and thus the theoretical
difficulties of the art exceedingly simplified, if not altogether done away. The
following rule will be found to be universal, and applicable to every possible case; The
point to which any straight line in nature appears to tend, is that point in the medium
whether plane or cylindrical, where a visual ray parallel to that line would fall. And then
by corollary; All lines which are parallel in nature, must, in a drawing, be made to converge
to the same point: and further; All lines which are horizontal in nature, must tend
to some point in the * horizontal l in e a n d those which actually incline downwards, must
in a picture be drawn to some point below that line, and those upwards, to some point
above.
It is not only in pictures of buildings, that a knowledge of the principles of perspective
is necessary, although in such it is absolutely indispensable; but, in every branch of
the art of drawing, it is eminently useful; a consideration which has occasioned the subject
to be noticed in this place. In confining this explanation to the space of a note, many
particulars must necessarily be omitted which might perhaps make the above remarks
more available to those who are but little acquainted with die dieory of the art; but this
exposition of the principles which guided my own practice, will, it is hoped, be sufficiently
intelligible to those who take any particular interest in the subject.