102 THE ROYAL SOCIETY OF CANADA 



single sine-wave of 24-hours period than does the diurnal curve at 

 Agincourt. 



In plate II is shown graphically the seasonal Diurnal curves for 

 each station in heavy line and the first four harmonics in light lines. 



In addition to these regular daily movements there are also recorded 

 what are known as magnetic disturbances. These do not occur at 

 any apparent regular intervals in any year nor do they show similar 

 movements at similar local times, but usually at the same absolute 

 times the movements are more or less synchronous and in the larger 

 storms obscure completely the daily movement. 



In plate III examples of different types of disturbance are repro- 

 duced. In figures I and II that type of disturbance having a sudden 

 commencement occurring at the same instant of absolute time is 

 shown. A small westerly movement is followed by a much larger 

 easterly movement at both stations, and the disturbance is immedi- 

 ately in full progress. In figure III at Agincourt there is a rather 

 leisurely movement of the magnet whilst at Meanook we have a 

 sudden increase at 8h 30m G.M.T. followed by a storm with very 

 large and rapid fluctuations which on the average have carried the 

 magnet in the opposite direction to the movement at Agincourt. In 

 figures IV to VII is shown the type of disturbance which is usually of 

 short duration and produces what is known as a bay in the magnetic 

 curve. There is very often a recurrence of this bay on the following 

 day at about the same time as shown in figure IV. Figure V shows the 

 bay in the opposite direction at the two places. In figure. VI the bay 

 is westerly, but while a smooth curve is recorded at Agincourt, it is 

 serrated at Meanook. In figure VII the bay is easterly. In figure 

 VIII a magnetic storm of large amplitude is shown for Meanook with 

 practically no corresponding movement at Agincourt. 



