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CHAPTER XVI. 
OF THE CONSTRUCTION OF THE BALISTA. 
I HAVE explained the structure of catapultæe, their parts 
and proportions. The constructions of balistæe are va- 
rious and different, though contrived to produce similar 
effects. Some of these are worked by windlasses, others 
by systems of pulleys, others by capstans, and others by 
wheels : no balista, however, is made without regard to 
the weight of the stones it is intended to throw. Hence 
the rules will only be understood by those who are ac 
quainted with arithmetical numbers and their powers. 
For instance, holes are made in the capitals, and through 
them are brought the cords, made either of woman's 
hair, or of gut, which are proportioned to the weight of 
the stone that the balista is to throw, as in the catapultæe 
the proportions are derived from the length of the arrow. 
But that those who are not masters of geometry and 
arithmetic, may be prepared against delay on the occa- 
sions of war, I shall here state the results of my own ex- 
perience as well as what I have learnt from masters, 
and shall explain them, by reducing the Greek measures 
to their correspondent terms in our own. 
CHAPTER XVII. 
OF THE PROPORTIONS OF THE BALISTA. 
A BALISTA capable of throwing a stone of two pounds 
should have the hole (foramen) in the capital five digits 
wide ; for a stone of four pounds, six digits ; for a stone 
of six pounds, seven digits ; for a stone of ten pounds, 
eight digits ; for a stone of twenty pounds, ten digits: