ON ROMAN AQUEDUCTS. 345 



supposing that they had any idea of the necessity of making the 

 water in the reservoir from which the distribution took place 

 remain at a constant height, or, to use Prony's own expression, 

 of making it stagnate. It is quite true, that Fabretti asserts 

 that the measurements were made in the piscinse, where the 

 water was comparatively speaking at rest, but although mea- 

 surements in the piscina were undoubtedly made, yet it is quite 

 clear that Frontinus had no scruple as to the propriety of mea- 

 suring the section of a running stream, calculating its area in 

 quinarise by a process of simple reduction, and then assuming 

 the result as an expression of the number of quinariae which the 

 stream was capable of supplying. This is so evident, that Prony 

 remarks that Frontinus could have had but vague ideas as to 

 the efflux of fluids, and that a method which took no account of 

 the velocity of the stream must have led to strange results. He 

 adds, and rightly, that Frontinus appears to have avoided mak- 

 ing his measurements in places where the velocity was small. 

 Nor is this inconsistent with Fabretti' s remark as to measure- 

 ments in piscinas, for we do not in reality know that the water 

 was in any sense reduced to rest in the places in which these 

 measurements were made. 



The same conclusion, namely, that one of the conditions 

 which Prony speaks of as essential, was not attended to at all, 

 appears from the passage in which Frontinus describes the posi- 

 tion which the calix ought to occupy with respect to the stream of 

 water in which it is placed. The passage is obscure, but a stream 

 is plainly spoken of. A third consideration would lead to the 

 same result. I refer to the description which Yitruvius gives of 

 the three basins immediately supplied from the castellum. From 

 two of these there appears to have been a waste pipe into the 

 third; a circumstance which it is hard to reconcile with the 

 supposition that the surface was kept at a constant level by 

 means of pipes employed in its ulterior distribution. 



In this respect then at least the system of the Komans ap- 

 pears to omit one of the conditions which in modern times have 

 been found necessary, and there is at least another point in 

 which the discrepancy between their practice and ours deserves 

 to be noticed. It is well known, that if water escapes from an 

 orifice in the side of a vessel, the quantity discharged will, other 

 things remaining alike, vary with the length of the adjutage, as 



