97 
of Edinburgh , Session 1872-73. 
resistances found. The spec. res. of the saturated solution is 
29*3 B.A.XJ. The solution of maximum density is that also of 
maximum conductivity. The curve (described as above) is an 
hyperbola whose asymptotes are inclined at an angle less than a 
right angle. 
Nine solutions of potassium bichromate, and nine also of potassium 
sulphate, were investigated. The resistances in both decrease up 
to the point of saturation, the least being, in the former, 29 - 6 B.A.U., 
and in the latter, 16'6 B.A.U. The curves are both hyperbolas; 
that of the bichromate has its asymptotes approximately perpen- 
dicular to one another, and that of the sulphate has them inclined 
at an angle greater than a right angle.* 
Fifteen mixtures of equal volumes of solutions of copper and 
zinc sulphates were also examined. In all cases, the resistance of 
the mixture is less than the mean of the resistances of its com- 
ponents. The lowest spec. res. of any of the mixtures prepared, is 
27*3 B.A.U., and it consisted of equal volumes of the two saturated 
solutions. The zinc sulphate appears to exercise the greater 
influence in the determination of the spec. res. of the mixtures. 
3. On the Effect of Heating one Pole of a Magnet, the other 
being kept at a Constant Temperature. By D. H. Mar- 
shall, Esq., M.A., and C. G. Knott, Esq. Communicated 
by Professor Tait. 
The following are a modification of some experiments conducted 
in the summer of 1871, and communicated to the Society on the 
15th of January 1872. These consisted in heating a magnet uni- 
formly throughout, and then noting the change in magnetic 
strength. Those conducted this winter consisted in heating one 
pole of a magnet, while the other was kept at a temperature as 
nearly constant as possible, and then noting the change of mag- 
netic strength in both poles. The arrangement adopted was the 
same in both series of experiments, only being double in the latter. 
It consisted in having a magnet set magnetically east and west, 
each end of which passed through a cork fitted into a hole made 
* For all four salts formulae are given, by means of which the conductivity of 
any solution may be calculated if its density is given. 
