COPPER SULPHATE — ALGEBRAIC CURVES. 257 



•000121. The values of o and j3 are fairly constant for all 

 concentrations, but not quite so. The mean values ^ive a 

 maximum conductivity at 115° C, but this position is not 

 constant, as it is sometimes below 100°. Its position seems 

 to vary with very small impurities. 



The relation between concentration and conductivity is 

 given by the formula tc = an^ where n is the percentage of 

 salt in the solution, and a and b are constants, a = "00403, 

 h = -766. The general expression for the conductivity thus 

 becomes k = '00403 x n-"'^^' (1 + -0229^ - -0001 2 k«). 



II. Effect of pressure on conductivity. These results only 

 apply to pressures not greater than atmospheric. The ex- 

 periments were hardly more than qualitative, but, indicated 

 the following facts : — 



I. The conductivity under atmospheric pressure is 

 much less than that under the pressure of a few 

 cms. of mercury. 

 II. There is probably a minimum conductivity at a 



pressure of about 65 cms. 

 III. The fall is much more marked in strong solutions 

 than in weak ones, the total decrease varying 

 from 9 to 18 per cent, of the whole amount. 



3.— ON A PROPERTY OF ALGEBRAIC CURVES. 



By J. H. MICHELL. 



[^AbstractJ] 



The author showed, by the use of complex variables, that 

 the following theorem was true of an algebraic curve of the 

 //.*'' degree : — 



A circle being drawn through a fixed point to cut the curve 

 in 2" points and these joined by n chords, tlte product of the 

 perpendiculars from the fixed point on the chords is constant, 

 being independent of the size and position of the circle, and a 

 function merely of the position of the fixed point. 



