The most convenient 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[1] actus. Where the water is wanted to ascend[2] 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[3] the pipe is five fingers in circumference 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"[4] 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."[5] 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,[6] too, for branches should be made as circumstances may demand.