328“ 
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 simi¬ 
lar 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 
acquainted 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 catapultae 
the proportions are derived from the length of the arrow. 
But that those who are not masters of geometry and arith- 
metic, may be prepared against delay on the occasions of 
war, I shall here state the results of my own experience 
as well as what I have learnt from masters, and shall ex¬ 
plain them, by reducing the Greek measures to their cor- 
respondent terms in our own.