WATER SUPPLY. 59 
retires from its shore, and the slopes being exceedingly gentle the area of 
the lake is rapidly contracted. The surface for evaporation diminishes and 
its ratio to the inflow becomes less. As the water rises the surface of the lake 
rapidly increases, and the ratio of evaporation to inflow becomes greater. 
In this way a limit is set to the oscillation of the lake as dependent on the 
ordinary fluctuations of climate, and the cumulation of results is prevented. 
Whenever the variation of the water level from its mean position becomes 
ereat, the resistance to its further advance in that direction becomes pro- 
portionally great. For the convenience of a name, I shall speak of this 
oscillation of the lake as the limited oscillation. It depends on an oscillation 
of climate which is universally experienced, but which has not been found 
to exhibit either periodicity, or synchrony over large areas, or other features 
of regularity. 
Beside the annual tide and the limited oscillation, the lake has been 
found to exhibit a third change, and this third or abnormal change seems 
to be connected with the increase of the tributary streams. In order to 
exhibit it, it will be necessary to discuss somewhat fully the history of the 
rise and fall of the lake, and I shall take occasion at the same time to call 
attention to the preparations that have recently been made for future 
observations. 
Previous to the year 1875 no definite record was made. In 1874 
Prof. Joseph Henry, secretary of the Smithsonian Institution, began a 
correspondence with Dr. John R. Park, of Salt Lake City, in regard to the 
fluctuations and other peculiarities of the lake, and as a chief result a 
systematic record was begun. With the codperation of Mr. J. L. Bartoot 
and other citizens of Utah, Dr. Park erected a graduated pillar at Black 
Rock, a point on the southern shore which was then a popular summer 
resort. It consisted of a granite block cut in the form of an obelisk and 
engraved on one side with a scale of feet and inches. It was set in gravel 
beneath shallow water, with the zero of its scale near the surface. ‘The 
water level was read on the pillar by Mr. John T. Mitchell at frequent 
intervals from September 14, 1875, to October 9, 1876, when the locality 
ceased to be used as a watering place, and the systematic record was 
discontinued. Two observations were made by the writer in 1877, and it 
