ental practice with crayon and lead pencil),
you shall try to draw a line of absolute correctness with the point, not
of pen or crayon, but of the brush, as Apelles did, and as all coloured
lines are drawn on Greek vases. A line of absolute correctness, observe.
I do not care how slowly you do it, or with how many alterations,
junctions, or re-touchings; the one thing I ask of you is, that the line
shall be right, and right by measurement, to the same minuteness which
you would have to give in a Government chart to the map of a dangerous
shoal.

142. This question of measurement is, as you are probably aware, one
much vexed in art schools; but it is determined indisputably by the very
first words written by Lionardo: "Il giovane deve prima imparare
prospettiva, _per le misure d'ogni cosa_."

Without absolute precision of measurement, it is certainly impossible
for you to learn perspective rightly; and, as far as I can judge,
impossible to learn anything else rightly. And in my past experience of
teaching, I have found that such precision is of all things the most
difficult to enforce on the pupils. It is easy to persuade to diligence,
or provoke to enthusiasm; but I have found it hitherto impossible to
humiliate one clever student into perfect accuracy.

It is, therefore, necessary, in beginning a system of drawing for the
University, that no opening should be left for failure in this essential
matter. I hope you will trust the words of the most accomplished
draughtsman of Italy, and the painter of the great sacred picture which,
perhaps beyond all others, has influenced the mind of Europe, when he
tells you that your first duty is "to learn perspective by the
_measures_ of everything." For perspective, I will undertake that it
shall be made, practically, quite easy to you; if you care to master the
mathematics of it, they are carried as far as is necessary for you in my
treatise written in 1859, of which copies shall be placed at your
disposal in your working room. But the habit and dexterity of
_measurement_ you must acquire at once, and that with engineer's
accuracy. I hope that in our now gradually developing system of
education, elementary architectural or military drawing will be required
at all public schools; so that when youths come to the University, it
may be no more necessary for them to pass through the preliminary
exercises of perspective than of grammar: for the present, I will place
in your series e