On the Waters of the Salt Lake of Urmi. 



313 



by its Secretary, 184 years ago. Edmund Halley, in his "Short 

 Account of the Cause of the Saltness of the Ocean, and of the several 

 Lakes that emit no Rivers," expressed himself as follows : — " I recom- 

 mend it therefore to the Society, as opportunity shall offer, to procure 

 the Experiments to be made of the present degree of Saltness of the 

 Ocean, and of as many of these Lakes as can be come at, that they may 

 stand upon Eecord for the benefit of future Ages."* At the present 

 day there are additional reasons for recording the properties and com- 

 position of such salt lakes as are known to be inhabited by life, because 

 Schmankewitschf and many others of the modern school of Eniwickel- 

 ungsmechanih (Morgan, Loeb, Vernon, &c.) have proved that every 

 change in the salinity of the waters is accompanied by definite, rapid, 

 and corresponding changes in the anatomical structure of certain of 

 their halophilous fauna, and especially of the species of Artemia, one 

 of which occurs in Lake Urmi.| 



The superficial area covered by Lake Urmi is about 1750 square 

 miles, or about four times that of the Dead Sea. For so large an expanse 

 of water its depth is inconsiderable ; the greatest soundings do not 

 exceed 40 feet, and since much of the lake is extremely shallow, its 

 average depth is probably under 20 feet. When viewed from the 

 commanding heights of one of its islands, its waters show that brilliant 

 deep blue colour which is so characteristic of salt lakes, but as seen 

 from a boat, the light which is reflected from the light grey mud at the 

 bottom is green. 



The temperature of so small a volume of water, which is at the same 

 time so extended as Lake Urmi, must necessarily vary considerably with 

 the seasonal changes of temperature. During the months of July and 

 August the temperature of the surface waters varied from 27*8° C. to 

 25*8° C, and the temperature of the bottom water at a depth of about 

 25 feet was 25° C. The specific gravity of the water, as measured on 

 the spot by an ordinary hydrometer, was I'll, whether the water was 

 drawn from near the bottom or from the surface of the lake ; it may 

 therefore be assumed that the waters of the lake remote from the 

 mouths of the fresh water tributaries were of a fairly uniform density, 

 a result which was probably due to the thorough mixing of the waters 

 produced by the strong south-easterly breezes prevalent at the time. 



The total quantity of water available for the more detailed examina- 

 tion was brought home in two glass wine bottles, holding about f litre 

 a-piece. The samples A and B were collected on September 16, 1898, 

 near the base of the Bezau Daghi, on the western shore of the lake, 

 where there is comparatively deep and clear water close in shore. The 

 bottles were carefully corked, and it is, I think, fair to assume that no 



* ' Phil. Trans.,' vol. 29, p. 299, 1715. 

 f - Zeitschrift Wiss. Zoologie,' vol. 25, 1875. 

 X Griinther, ' Nature,' vol. 58, p. 435. 

 VOL. LXV. 2 A 



