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Page:Frontinus - The stratagems, and, the aqueducts of Rome (Bennet et al 1925).djvu/425

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Aqueducts of Rome, I. 27–30

employed, whenever several quinariae are delivered by one pipe and received in a reservoir, from which consumers receive their individual supply,—this being done in order that the conduit may not be tapped too often.[1]

The second principle is followed, whenever the pipe does not increase according to some necessary multiple of quinariae, but according to the size of diameters, in conformity with which principle they enlarge their capacity and receive their names; as for example, when a quarter [of a digit] is added to the diameter of a quinaria, we get as a result the senaria,[2] but its capacity is not increased by a whole quinaria, for it contains a quinaria plus 5/12 plus 1/48. So on, by adding successive quarters of a digit to the diameter, as was said above, we get by gradual increases, a 7-pipe (septenaria), an 8-pipe (octonaria), and up to the 20-pipe (vicenaria).

After that[3] we have the method of gauging which is based on the number of square digits contained in the cross-section, that is, the orifice of each ajutage, from which number of square digits the pipes also get their names. Thus those which in cross-section, that is, in circular orifice, have 25 square digits, are called 25-pipes. Similarly we have the 30-pipe (tricenaria), and so on, by a regular increase of 5 square digits, up to the 120-pipe.

In the case of the 20-pipe, which is on the border line between the two methods of gauging,[4] the two methods almost coincide. For according to the

  1. ↑ Frontinus merely means that, instead of tapping the main conduit for individual consumers, the Romans delivered a given number of quinariae to a reservoir, from which the water was delivered to the consumer.
  2. ↑ It seems advisable to restate, for clearness' sake, the two principles of increase referred to by Frontinus. In the first class we have pipes, whose capacity is some multiple of the quinaria. In the second class, we have an ascending series of pipes each of which increases beyond the next smaller by a diameter of 1/4 inch. In other words the first class is based on multiples of volume; the second on slight increases in diameters.
  3. ↑ i.e. for the pipes above the 20-pipe.
  4. ↑ i.e. those mentioned in 28 and 29.
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