247 
and necessary, and déscribed them in my treatise on 
dialling: in this place I confine myself to those which 
act by the impulse of water. The others, which are 
more for pleasure than utility, may be seen by the 
curious in the writings of Ctesibius. 
CHAPTER XIII. 
OF WATER ENGINES. 
I CANNOT here omit a brief explanation, as clearly as 1 
can give it, of the principles on which hydraulic organs 
are constructed. A base of framed wood-work is pre- 
pared, on which is placed a brazen box. On the base, 
right and left, uprights are fixed, with cross pieces like 
those of a ladder, to keep them together ; between which 
are enclosed brass barrels with moveable bottoms, per- 
fectly round, having iron rods fixed in their centres, and 
covered with leather and wool, attached by pins to the 
levers. There are also, on the upper surface, holes 
about three inches diameter, in which, near the pin-joint, 
are brazen dolphins with chains hanging from their 
mouths, which sustain the valves that descend below the 
holes of the barrels. Within the box, where the water 
is deposited, there is a species of inverted funnel, under 
which two collars, about three inches high, answer the 
purpose of keeping it level, and preserving the assigned 
distance between the lips of the wind-chest and the 
bottom of the box. On the neck a chest, framed to- 
gether, sustains the head of the instrument, which in 
Greek is called kavov uoòs (canon musicus) ; upon 
which, lengthwise, are channels, four in number, if the 
instrument be tetrachordal, six if hexachordal, and eight 
if octochordal. In each channel are fixed stops, that are