Page:Baylee's Method of Finding the Longitude.djvu/12

year, with respect to any other meridian, B, will give the difference of longitude between any places which are under the two meridians A and B. For, the diurnal motion of the earth on its axis being equable and uniform, at least so far as has been hitherto practically noticed, it follows, that equal relative spaces of the firmament must pass over equal and absolute spaces of the earth's surface in equal times. The times of the respective culminations should be found by observation, and not by calculation only.^[1]

To find the Variation:—When the meridian is found the variation is found: but the meridian has been found, by the method here presented, and therefore the variation is found.^[2]

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In the Advertisement and in the Notes to this Method, some expressions, such as "the efficiency of my method," may appear as originating from self-sufficiency; but I can with truth assure my readers they have originated from the opposite principle. Attached to the system I had studied, the reflection of many years had influence scarcely sufficient to induce me to depart from it in any degree; because the high respect I cherish for the distinguished characters who had

1. The mean motion of the sun is stated to be about fifty-nine minutes of a degree for each day; because as every circle, according to the English division, contains 360 degrees, and as our years are between 365 and 366 days, therefore,
   Days.
   365
   plus :
   Degrees.
   360
    ::
   Day.
   1
    :
   Minutes.
   59 plus.
   But this mean is taken on the presumption of the annual motion being equal and uniform, in equal times, through the entire orbit; but a slight inspection of the sun's right ascension (to go no further), as presented in the Nautical Almanack, will be quite sufficient to prove the absurdity of applying this mean in particular cases; and I need not hesitate to say, that the irregularity of the earth's annual motion has a sensible effect on the earth's diurnal motion on its axis; which effect, I apprehend, demands particular notice.
2. I shall reserve my observations on the variation of the compass for another occasion, as I wish to enter more largely on it than I can do at this moment, in consequence of the pressing demands of a large family, to whom my absence, which has been already too long, may be highly injurious.