THE ARTESIAN WATER SUPPLY OF EASTERN FLORIDA.

the pipe are necessarily approximate measurements. Not only does the water lose in temperature in moving to the mouth of the pipe, but it mingles with the higher and colder waters entering the pipe which necessarily equalizes the temperature of the whole. They show, however, increase of temperature with increase of depth.
LOSS OF HEAD AND REDUCTION IN FLOW.
Exact measurements of loss of head and reduction in flow in artesian wells are usually difficult to obtain. In the case of the Jacksonville city water supply, fortunately measurements of flow have been taken at intervals from the time the first wells were put down in 1885 to the present time. These measurements kept through a period of 24 years afford records of especial interest and value. The following table of flow was supplied by Capt. R. N. Ellis, Superintendent of the Jacksonville city water supply. Two basins are used to receive the flow known as the north basin and the south basin. The wells are grouped in the table according to the basin into which they flow. The wells are numbered chronologically in the order of the date when completed.
This table shows conclusively that although the rate of flow is variable for different wells and for the same wells at different periods, yet in this group of wells there is a continuous and progressive loss of flow. That the same is true of other wells throughout this area there can be no reasonable doubt. Those who give no special attention to their wells suppose as a rule that the flow remains unaffected indefinitely. Many other well owners, however, have observed this loss in flow with succeeding years. The reduced flow is best observed near the margin of the flowing area in wells located on somewhat elevated ground. Many of the wells from which the water will flow only a few feet above the surface when first drilled may in time cease to flow. In these cases the pressure which originally caused the flow having been partly relieved, the water no longer rises above the surface of the ground.
Exhaustion and ultimate failure of an artesian reservoir is not unknown. It is probably true that in nearly all artesian seetions the original pressure gradient in the water-bearing rock is appreciably lowered by the drafts made upon the subterranean supply,with a consequent actual decrease in the capacity of the wells. In this connection Professor C. S. Slichter states.* "It must be kept well in mind that there is a limit to the amount of water that can be withdrawn from an artesian basin. There is no such thing as an inexhaustible supply in this connection. The
*U S. Geol. Surv., Water Supply Paper, No. 67, p. 94, 95, 1902.

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