The smaller pipes which led from the main to the houses of private persons, were called

punctoe ; those inserted by fraud into the duct itself, or into the main after it had left the castellum, fistula, illicitce.

The erogatio was regulated by a tube called calix, of the diameter required, attached

22 PRELIMINARY ESSAY.

to the extremity of each pipe where it entered the castellum ; it was probably of lead in the time of Vitruvius, such only being mentioned by him but was made of bronze ;

of the aquarii, who were (aneus) when Frontinus wrote, in order to check the roguery able to increase or diminish the flow of water from the reservoir by compressing or extending the lead. Pipes which did not require any calix were term ed solutce* The fact referred to in the last paragraph, of the increase and diminution of the quantity of water flowing through a tube, by altering its shape, is of sufficient interest to authorise some further notice of it. It must be stated in the first place, that more water

will flow through a short tube than through a simple orifice of the same diameter. It

may be thus ascertained : bore a hole of an inch diameter in a bucket, plug it up, and,

having filled the bucket with water, withdraw* the plug. On examination of the stream that issues from the hole, it will be found to taper off considerably at half an inch from the distance of half the diameter of the hole. If a short tube of the same diameter be inserted in the hole, the discharge of water will be greatly increased, and if at the distance of not more than two or three diameters, this tube should be made to flare gradually, or assume a conical shape, the volume of water passing would be more than doubled, as compared with the discharge throvigh the hole, without any tube.