From the laft Table it appears, that when the variation was firft obferved, the north pole of the magnetic needle declined eastward of the meridian of London; but it has fince that time been advancing continually towards the weft; fo that in the year 1657, the magnetic needle pointed due north and fouth. At prefent it declines about 24° weftward, and it seems to be ftill advancing towards the welt. It appears likewife, that the annual variation is by no means regular, and fuch is likewife the cafe with the daily or hourly variation; which though evidently influenced by heat and cold, does not however follow any known law. The first of the following Tables contains a fpecimen of hourly variation, as obferved by the late ingenious Mr. Canton, F. R. S. The fecond fhews the mean variation for each month in the year, as deduced from the fame Mr. Canton's numerous obfervations*. * Philofophical Tranfactions, vol. LĮ. The |