From Della Tramutatione Metallica by Giovanni Battista Nazari (Brescia, 1599, new edition of the 1564 original).
This amazing drawing could perhaps be considered as the first application of a graph abstraction. Heads stand for vertices and snake's bodies for edges.
The harmonic evolution
digraph is peculiarly balanced:
it consists of trees of height 1,2 4, and loops
of length 1, 2, 4:
| Loops | = | 64 L1 + 96 L2 + 192 L4 | |
| Tree | = | T1 * T2 * T4 |