Lovering on Magnetic Observations at Cambridge. 149 
general period. In our former communication, this opinion was 
advanced on the strength of limited comparisons made between 
Cambridge and Toronto, and the authority of others who had 
given attention to the same point. But the proof is accumulated 
to a demonstration in the volume of Colonel Sabine, where we 
have the comparison of Toronto with Prague, in the heart of 
Europe, and Van Diemen’s Land; and, on some occasions, with 
the Cape of Good Hope, St. Helena, and the wastes of the 
Southern waters. The practice of these Observatories has been, 
to watch the instruments with great care, whenever the changes 
exhibited any extraordinary extent or frequency. Mr. Sabine 
finds from the records, that out of twenty-nine principal distur- 
bances, in 1841], the largest number manifested themselves under 
various modifications at the three first mentioned stations, and 
that the days of greatest disturbance in the year were the same 
at each. It is further observed, that on thirteen days out of the 
twenty-four days of unusual disturbance at Toronto, in 1841, the 
Aurora was visible, and that all these days were marked by 
magnetic disturbances at Prague and Van Diemen’s Land. On 
the remaiping thirteen days, the sky at Toronto was so far over- 
cast that the Aurora could not have been seen, on the suppo- 
sition that it existed. Mr. Sabine concludes that the Aurora, 
which has long been associated, in the time of its appearance, 
with local magnetic changes, must now be considered as more 
especially a local manifestation of those grand magnetic hurri- 
canes which swell over large portions of the planet, breaking 
furiously upon certain favored spots, and acting nearly simulta- 
neously in places widely separated from each other. 
As some of the magnetic Observatories had ,not gone into full 
operation till the commencement of 1841, the comparison is limited 
to that year. It would have been desirable to have included Cam- 
28 
