ON ROMAN AQUEDUCTS. 351 



was really adopted ; but if the waters in the reservoirs rose and 

 fell, the depths of the pipes below the surface must have varied, 

 for the position of the pipe was plainly fixed. We know so 

 little about matters of detail, that much stress cannot be laid 

 upon what I have mentioned, but the difficulty of shifting the 

 pipes, and the absence of any information as to how the water 

 in the reservoir was kept at a constant level, are worth consider- 

 ing. 3rdly, This would account for the absence of any state- 

 ment as to the quantity of water delivered by a quinaria. The 

 question, how much does sucji a pipe deliver in twenty-four 

 hours, must have occurred to the most unthinking person, if any 

 steps had been taken to make the quantity constant. 4thly, 

 Frontinus speaks of a case in which the erogation had ceased, 

 on the ground that the modulus was exhausted a passage 

 which would be easily understood, if we suppose that from a 

 deficient supply the water had sunk below what was accounted 

 low- water level. 



5thly. The fraud imputed to the aquarii of making the 

 large pipes too large would thus appear to have at least had its 

 origin in a reasonable principle of compensation. For if the 

 lowest point of six vicenarias, and that of one pipe of 120 square 

 digits were all on the same level, the six small pipes, though 

 nominally equivalent to the one large one, would, by having 

 their centres lower, deliver a great deal more water, and it 

 would be easy to calculate the circumstances under which they 

 would be equivalent to the larger pipe which the aquarii sub- 

 stituted for one of 120 digits. Lastly. The old French water 

 system would then be an improvement on the Roman, and not a 

 retrocession from it. The former seems to run so far back in 

 the middle ages that we may fairly suppose it traditionally con- 

 nected with the Roman. The transition is easy, and may not 

 improbably have been made at Rome itself. You have only to 

 take the pipe out of the reservoir so as to allow the efflux of water 

 to be free, and to let the water just rise so as fairly to cover the 

 whole aperture. This with making the standard modulus one 

 inch would in effect be the old French system, which may easily 

 have suggested itself in answer to a question what would be 

 the discharge through a given opening when its mensura was 

 just filled and no more, and the disturbing influences (due to 

 the direction of the pipe, &c.) removed ? 



