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

 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.

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, but its capacity is not increased by a whole quinaria, for it contains a quinaria plus $1⁄4$ plus $5⁄12$. 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 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, the two methods almost coincide. For according to the 