and consideration. They can hardly upset the conclusion 
arrived at in this paper, that the greater part of the diurnal 
variation is due to disturbing causes outside the earth s 
surface. I forbear at present from entering into some very 
curious conclusions to which we seem almost forced if we 
adopt this view. 
It will be interesting to apply the method here used to 
the other periodic variations of terrestrial magnetism which 
have been discovered. 
COKRIGENDUM. 
Page 73, line 4, for extended read extruded. 
