312 



Messrs. E. T. Giinther and J. J. Manley. 



of separating the two metals, and also of isolating nickel from other 

 metallic impurities. Further, the discrepancy between the increment 

 values of the author and of Fizeau for these metals is only of the same 

 order as that between the concordant values of the author and of 

 Benoit, 0*46, on the one hand, and of Fizeau, 0*76, on the other, for 

 the 10 per cent, alloy of platinum-iridium, the value for which Fizeau 

 gives in the same table referred to. 



Taking, therefore, the values published by Fizeau for the increments 

 of nickel and cobalt as correctly representing the results of his experi- 

 ments, his values of the coefficients at 0°, the constants a, calculated by 

 use of the increment, are as under : — 



Nickel a = O'OOO 012 51 



Cobalt a = O'OOO 012 04 



j» Percentage difference 3*8. 



At 100° the coefficients would become — 



Nickel a = 0*000 013 22 1 ^ ., r „. 



Cobalt a = 0-000 012 84 j Percenta S e dlfeence 2 ' 9 ' 



The values thus calculated for the expansion at 0° from Fizeau's 

 data are almost identical with the author's values. But the consider- 

 able difference between the values and the order of the increments now 

 given and those of Fizeau introduces a different order of progression 

 with rise of temperature. According to Fizeau the difference between 

 the coefficients of the two metals is a diminishing one, the percentage 

 difference having fallen from 3*8 at 0° to 2*9 at 100°; whereas the 

 author's determinations indicate that the difference is an accelerating 

 one, rising from 3*2 per cent, at 0° to 4*3 at 100°. 



" On the Waters of the Salt Lake of Urmi." By E. T. Guhther, 

 M.A., and J. J. Manley, Daubeny Curator, Magdalen College. 

 Communicated by Sir John Mueeay, F.E.S. Eeceived June 

 8— Eead June 15, 1899, 



In June, 1897, a portion of the Government Grant was allotted to 

 one of the authors by the Committee of the Eoyal Society, for the 

 investigation of the fauna and flora of the great salt lake of Urmi, in 

 Persia, as well as of the relations of that fauna and flora to its environ- 

 ment. The present research was undertaken with the view of placing 

 on record some of the conditions prevailing in the lake at the present 

 day. 



The extraordinary changes which the level of the waters of the lake 

 has undergone, and is still undergoing, enhance the importance of 

 periodical examinations of the nature of the waters. The advisability 

 of the preservation of such records was urged upon the Eoyal Society 



