494 PLINTHS NATURAL HISTOET. [Book XXXI, 
CHAP. 31. (6.) THE METHOD OF CONVEYING WATEE. 
The most conyenient method of making a watercourse from 
the spring is by employing earthen pipes, two fingers in thick- 
ness, inserted in one another at the points of junction — the one 
that has the higher inclination fitting into the lower one — and 
coated with quick-lime macerated in oil. The inclination, to 
ensure the free flow of the water, ought to be at least one-fourth 
of an inch to every hundred feet ; and if the water is conveyed 
through a subterraneous passage, there should be air-holes let in 
at intervals of every two^^ actus. "Where the water is wanted 
to ascend^^ aloft, it should be conveyed in pipes of lead : 
water, it should be remembered, always rises to the level of its 
source. If, again, it is conveyed from a considerable distance^ 
it should be made to rise and fall every now and then, so as 
not to lose its motive power. The proper length for each 
leaden pipe is ten feet ; and if the pipe is five fingers in cir- 
cumference its weight should be sixty pounds ; if eight feet, 
one hundred ; if ten, one hundred and twenty ; and so on in the 
same proportion. 
A pipe is called *'a ten-finger"^ pipe when the sheet of 
metal is ten fingers in breadth before it is rolled up ; a sheet 
one half that breadth giving a pipe of five fingers.''^' In all 
sudden changes of inclination in elevated localities, pipes of 
five fingers should be employed, in order to break the impetu- 
osity of the fall : reservoirs, too, for branches should be made 
as circumstances may demand. 
CHAP. 32 HOW MINEHAL WATERS SHOULD BE USED. 
I am surprised that Homer has made no^^ mention of hot 
springs, when, on the other hand, he has so frequently intro- 
duced the mention of warm baths : a circumstance from which 
we may safely conclude that recourse was not had in his time 
to mineral waters for their medicinal properties, a thing so 
universally the case at the present day. Waters impregnated 
^•^ See B. xviii. c. 3, and the Introduction to Vol. III. 
In jets, he means. " Si quinarise erunt." 
56 ^' Denaria." ^'^ " Quinaria." 
5^ The name given to these reservoirs was ^' castellum or " dividicu- 
lum :" in French the name is " regard'' Vitriivius describes them, B. vii. c. 7- 
^ Pliny appears to have forgotten the warm springs of the Scamander, 
mentioned by Homer in the Iliad, B. xxii. 1. 147, et seq. 
