XIII. Note on a comparison of the diurnal ranges of magnetic declination at Toronto and Kew

Abstract

Through the kindness of the Science and Art Department, South Kensington, and of Mr. Carpmael, Director of the Toronto Observatory, we have received daily values (excluding Sundays) of the diurnal range of magnetic declination at Toronto. These observations extend from 1856 to 1879 inclusive, thus forming a series of twenty-four years. Each number is the difference in scale divisions of the declinometer between the greatest eastern and greatest western deflection of the declination magnet on each day, as observed at the hours 6 a. m., 8 a. m., 2 p. m ., 4 p. m ., 10 p. m., and midnight, of Toronto mean time, one scale division of the instrument being equal to 0,,72 nearly. It is probable that such differences represent very nearly the true diurnal range. Disturbances appear to be violent at Toronto, and we have rejected a few of the most disturbed observations, embracing those which denote ranges above forty scale divisions, or 28'.8. In all 107 observations were thus rejected in the series of twenty-four years. Although this rejection has been made, it must not be supposed that the remainder are entirely undisturbed, but are only freed from the excessive influence of a few violent disturbances. We have reduced in the meantime the sixteen years extending from 1858 to 1873, in order to compare them with a similar series of the Kew diurnal declination ranges, including disturbances.