error, forgetting that art consists in practice and theory. 
Theory is common to, and may be known by all, but the 
result of practice occurs to the artist in his own art only. 
The physician and musician are each obliged to have 
some regard to the beating of the pulse, and the motion 
of the feet, but who would apply to the latter to heal a 
wound or cure a malady? so, without the aid of the for¬ 
mer, the musician affects the ears of his audience by mo¬ 
dulations upon his instrument. The astronomer and 
musician delight in similar proportions, for the posi¬ 
tions of the stars, which are quartile and trine, answer 
to a fourth and fifth in harmony. The same analogy 
holds in that branch of geometry which the Greeks call 
oy oog: indeed, throughout the whole range of art, 
there are many incidents common to all. Practice alone 
can lead to excellence in any one: that architect, there¬ 
fore, is sufficiently educated, whose general knowledge 
enables him to give his opinion on any branch when 
required to do so. Those unto whom nature has been 
so bountiful that they are at once geometricians, astro¬ 
nomers, musicians, and skilled in many other arts, go 
beyond what is required of the architect, and may be 
properly called mathematicians, in the extended sense of 
that word. Men so gifted, discriminate acutely, and 
are rarely met with. Such, however, was Aristarchus of 
Samos, Philolaus and Archytas of Tarentum, Apollonius 
of Perga, Eratosthenes of Cyrene, Archimedes and Sco- 
pinas of Syracuse: each of whom wrote on all the 
sciences. Since, therefore, few men are thus gifted, and 
yet it is required of the architect to be generally well in¬ 
formed, and it is manifest he cannot hope to excel in each 
art, I beseech you, O Cæsar, and those who read this