74 METHODS AND RESULTS OF TORONTO OBSERVATIONS. 



years. Humboldt awards the distinction of having discovered the 

 changes in declination to Columbus, who on the 13th September, 

 1492, records the fact that in lat. 28 north and long. 28 west or 

 thereabouts, the direction of the needle changed from east of north 

 to west of north. It appears however, that the heathen Chinee was 

 aware of this fact as early as the twelfth century, for in a treatise by 

 a Chinese philosopher at this date it is distinctly stated that the 

 magnetised needle did not point north and south but always declined 

 to the east of south. 



It is the business of a permanent Observatory to watch and 

 record the changes which take place in the elements of magnetic 

 force. These changes are of three kinds, called secular changes, 

 periodic changes, and disturbances. 



The secular change is that which takes place from month to 

 month and year ,tu year, and taking the Toronto observations of 

 declination, the change has been from i° 14'' 3 west in 1841 to 3 

 51, west at the present time; the annual increase varying in amount 

 from i" 8 in 1848 to 7* 5 in 1875. The necessity for careful and 

 long continued observations is in this amply exemplified, as it must 

 be remembered that the charts on which ships are navigated have 

 the declination curves laid off on them, and have a fixed amount to 

 be applied as an annual increase or decrease to the declination laid 

 down, but this annual correction is a fluctuating quantity, hence 

 unless corrected from time to time errors would soon accumulate. 



The diurnal or first periodic range in declination has at Toronto 

 an amplitude of from eight to ten minutes of arc, the needle moving 

 rapidly from an extreme easterly position about 7 to 9 a.m., to an 

 extreme westerly one at 2 p.m., returning though with a minor curve 

 westwards, and generally remaining to the east of the mean position 

 all night. The other elements have also a regular daily fluctuation. 

 Disturbances are sudden and irregular fluctuations of the 

 magnet, some of which seem to be camparatively local whilst others 

 are practically universal ; changes of a similar character and almost 

 similar amounts occurring at Zika Wei, in China, at Toronto, at 

 Kew, in Great Britain, and at Melbourne, Australia, at almost the 

 same instant of time. Of the causes of these irregular movements, 

 or as they were christened by Baron Humboldt, magnetic storms, 

 little can at present be said that is not conjecture. This much may 



