579 
of Edinburgh , Session 1868-69. 
temperature on the thermometer scale, we have at once the tem- 
peratures of the warmest and coldest months, and the yearly 
temperature of the place, a knowledge sufficient for almost every 
purpose. This is best illustrated by an example. If we take from 
the isothermal chart the mean annual temperature of Paris, we 
find it 52°, and from the other chart its annual range is 30°; then 
the mean annual temperature plus the half of this range gives 67°, 
the July, and the mean annual minus half of the range, 37°, the 
January temperature of Paris. 
In conclusion, it is submitted that the chart of annual range is 
a useful companion to the isothermal chart, and that used together 
these two form a very complete guide to the temperature of the 
globe.* 
2. Note on Electrolytic Polarisation. By Professor Tait. 
The following note refers to some experiments instituted at the 
request of Mr Dewar, who asked me to determine the polarisation 
of the Palladium electrodes whose singular behaviour he recently 
described to the Society. 
I had just obtained one of Sir W. Thomson’s most recent forms 
of quadrant electrometer, and it occurred to me that this must be 
the proper instrument for determining polarisation, as its indi- 
cations are not affected by electric resistance, and give directly— 
that is, without assuming the truth of Ohm’s law for reverse elec- 
tromotive forces, and the consequent necessary determinations of 
resistance — the quantities required. The method employed by 
Wheatstone, Poggendorff, Buff, and others, assumes that the whole 
electromotive force in the circuit is the algebraic sum of those 
of the decomposing battery and of the electrodes, — an assumption 
whose truth some may consider to require proof, and which it is 
certainly useful to verify by an independent process. Again, after 
* The author has much pleasure in returning his best thanks to Mr Buchan, 
the Secretary of the Scottish Meteorological Society, for much assistance in 
the preparation of the materials for the chart, and for placing at his disposal 
a large private and unpublished collection of temperatures in all parts of the 
globe. 
