Royal Society of Edinburgh. 159 
of a disturbance is not so much a very great as a very rapid and 
abrupt departure of the magnet from the normal position; and 
since, on the theory of induction, the corresponding earth-current 
will be due to abruptness of magnetic change, we thus obtain an 
explanation why the currents which accompany disturbances are so 
very powerful, and also why these are as often positive as negative. 
With regard to the first class of earth-current observations, or 
those which occurred during magnetic calm, the author believed 
the daily range indicated by these observations to be the induction 
effect of the daily magnetic change, on which hypothesis the small 
value of the currents for the night hours might be accounted for 
by the corresponding fact that during these hours the magnetic 
change is exceedingly small. 
4. Note on a Pictish Inscription in the Churchyard of 
St Vigeans. By Professor Simpson. 
Dr Simpson considered the inscription to be “ Drosten, Son of 
Voret, of the family of Fergus.” 
o. On some Kinematical and Dynamical Theorems. By 
Professor W. Thomson. 
6. Note on a Quaternion Transformation. By Prof. Tait. 
Monday, 20th April 1863.—PrincipaL FORBES, V.P., 
in the Chair. 
The following Communications were read :— 
1. On the Conservation of Energy. By Professor Tait. 
2. On Fagnanis Theorem. By H. F. Talbot, LL.D. 
3. On the Theory of Parallel Lines. By H. F. Talbot, LL.D. 
An Address to His Royal Highness the Prince of Wales 
was adopted, and ordered to be forwarded to the Duke of 
Argyle for presentation. 
Royal Physical Society. 
Thursday, 26th February 1863.—Jamus M‘Bain, M.D., R.N., President, 
in the Chair. 
The following Communications were read :— 
I. On the Fossils of the Boulder Clay (Till) of Caithness. By Cuarues 
W. Peacu, Esq., Wick. 
Mr Peach gave details of the various kinds of shells that occur in 
