VITRUVIUS. 
266 
lirle iron pins (8), ulich the Greeks callepiscidat, ane diposed: then the ends of the 
rones (RS) are put through the holes (9) of the capitules, and thrown on the contary hde, 
where, being joined to the fucula (7), they are wound around it by the levers (7), lo that 
the diftended ropes, when struck by the hand, may on both parts yield an equal sound; they 
are then confined at the holes with wedges, that they may not lip. On the other side like- 
wise being passel through in the same manner, they are, by the levers and suculas, distended 
till hey sound equally. Thus, by the ropes being confined by the wedges, the catapultae are 
adjusted according to the rules of the musical tones. 
(15) This word has probably been miscopied, and 
should be read epizygidas; for it undoubtedly alludes to 
the epizygis hb, Fig. CII. which was laid on the modiols 
or choenices, and which is mentioned by that name in 
the foregoing chapter. 
(2*) This chapter explains the method of forming the 
tonus or combination of twisted cords, from whence the 
power of these engines was chiefly derived. 
For this purpose was used the machine F. CIV. called 
by Heron entonium. Vitruvius does not fully describe it. 
The two parallel beams ABCD were connected by the 
two transverse timbers UUVV, forming a rectangular 
frame, capable of receiving the capitule; the extremities 
of these transversals UUVV passed through the parallel 
beams ABCD, and had holes X, in which wedges Obeing 
driven, confined the capitule securely between the beams. 
The said capitule KLMN being then placed between 
the beams, with the two peritretae toward the two suculae 
FF, and the choenices or modiols P being fixed in the 
holes, as before described, one end Q of the cord was 
fastened to one of the epizyges, and the other end R 
carried through both choenices to the farthest sucula FF, 
to which it was fixed. The end of another cord S was 
also tied to the other epizygis, and in the same manner 
carried through both choenices to the other sucula F, and 
there fixed. Then both the suculae were turned around 
by the levers T, straining both the cords R and S, till they 
were diminished in their thickness a third part; and (as 
Vitruvius says) till both, upon being struck, yielded tones 
in unison. Wedges were then driven into the choenices, 
so as to secure the parts of the cords that were between 
the two choenices from slipping, and to preserve them in 
the same degree of tension. After this, the other parts of 
the cords were loosened from the suculae; convey ed round 
the epizyges, through both the choenices, in the same 
manner as before, and fastened to the opposite suculæe; 
by which they were distended till they were also in the 
same degree of tension as the former: and this was re- 
peated till the holes of the choenices were quite filled 
with the cords, and would admit no more. 
When the holes were so nearly full that it became 
difficult to put the cord through them, an iron pin 
called cestra, Fig. CV. polished and oiled, was driven in 
to open a passage; and then the cord was put through 
by the help of a polished iron needle called ramphis, 
Fig. CVI. having a hole near the point, through which the 
end of the cord was passed; and a knob at the other end, 
upon which the hammer struck to drive it through. 
The cording being completed, some of what remained 
of the cord was tied around the tonus, and the rest cut 
off. Then the end of the arm being introduced between 
the cords, the whole assemblage of cords was twisted, by 
turning round the choenices with the wrench, Fig. CIII. 
as before explained in the description of the balista. For 
wedging the cord in the choenices, the peristomis, Fig. CVII. 
was used ; it was a piece of wood about two or three 
palms long, having a cleft a in its side, just large enough 
to receive the cord. The peristomis was laid on the 
choenicis, and the cord inserted in the cleft, in which it 
was secured by a wedge b. The cord was usually prepared 
ready for use, and wound around a wooden roller, called 
epistomis, Fig. CVIII. 
Perrault, among many other remarks, observes that 
« it is difficult to comprehend how ropes of eight inches 
* thick, made of hair, should yield a tone sensible to the 
« human ear." This remark arose from his idea of these 
engines: he imagined that it was the whole tonus, or com- 
plication of twisted cords, that yielded the sound; whereas 
it was each separate cord of which that tonus consisted, 
as the foregoing account sufficiently explains. The in¬ 
tention of this was, that every cord of the tonus should be 
equally distended, and that the two hemitones should be 
equal in power: for if one were stronger than the other, 
the arm it held would recoil quicker, and act upon the 
missile before the other arm arrived; by which means the