aqueduct, -the velocity has several times been ascertained, though not in so perfect a manner as I intend to have it done, as soon as other duties will allow the time necessary. Sufficient data, however, have been ob- * As an illustration of the extreme sensibility of water to the smallest declivity, it may be stated that on a long reach of the Erie canal from Lockport, for a distance of sixty miles, the fall is only of half an inch in a mile, aqueducts had an .average declivity of one foot in six hundred. [Ei

CROfON AdUEDUCT. 215''

tained to show, that the capacity of the aqueduct for delivering water will be at least 15 I have not been much disappointed in per cent, greater than the calculated flow. finding the flow of water in the aqueduct, to exceed the calculation, as all my observations on the currents in canal feeders, have led me to believe the formulas laid down give rather less than the actual result. The flow of water through the pipes across Manhattan valley, and also the temporary pipe across Harlem river, being attended with circumstances somewhat different, has led some very intelligent persons to predict, that our expectations would not be realised in these cases it therefore maybe proper to observe that trial has ;

proved such predictions to have been not well founded, as the flow through the pipes has in a very exact manner corroborated the anticipated capacity, as compared with that in the aqueduct. -