6                    The Meafure of the Earth.

    not always found fo precife, and that it feenmed that it ought to
    have teen regularly a little lhortned in Winter and lengthened in
    Summer. But that however was but the ioth part of a Line) fo that
    having a refpedt to this variation, it has been judged beft to take
    the mean betwxeen them, and to take the length of 36 Inches 8'.
    Lines for the certain Meafure.
      If the length of' the Pendulum for feconds be once found expreft
    according to the ufual Meafure of every place, by this means may
    be had the proportion of the different Meafures fo exadc as if the
    originals had been compared, and this advantage would thence
    accrue, that for the fuiture any change therein might be difco-
    vered.
       But befides the particular Meafures, an agreement might be
    found of fuch as follow, which will need no other original but the
    Heavens.
       The length of a Pendulum of a fecond of the middle time might
    be called by the name of an Aftronomical Ray, the third of which
    Iblall be the univerfal Foot. The double of the Aifronomical Ray
    makes the univerfal Toife, which will be to that of Paris as 88r
    to 864.
      Four times the Aftronomical Ray may make the univerfal Perch
    equal to the length of a Pendule of two feconds.
       Finally the univerfal Mile may contain iooo Perches.
       Thefe univerfal Meafures fuppofe that the difference of places
    caufeth no fenfible variation to the Pendulums. 'Tis true, there
    have been made fome experiments at London, Lyons and Bolognia in
    Italy, by which it feems one might conclude that the Pendulums
    ought to be fhorter in fome proportion as the Aiquinodial is ap-
    proacht. Conformable to a conje6ture which has been formerly pro-
    pofed in the Affembly, that fuppofing the motion of the Earth,
    weights ought to defcend with lefs power under the Adquinodial
    than under the Poles. But we are not fulficiently informed of the
    juftnefs of thefe Experiments to make any conclufion thence. And
    we mutt befides note, that at the Hague, where the heighth of the
    Pole is greater than at London, the length of a Pendulum exa6tly
    determined by means of Clocks, was found the fame as at Paris.
    'Tis for this we advife thofe who would make experiment with a
    fingle Pendulum, to make ufe of great Pendulum Clocks, for that
    otherwife they will difficultly meet with the jufi Meafure. If it
    Ihould be found by experience that the Pendulum will be of diffe-
    rent lengths in different places, the fuppofition we have made con-
    cerning the univerfal Meafure drawn from the Pendulums, cannot
    hold, but this hinders not but that in every place there will be a
    perpetual and invariable Meafure.
       The length of a Parifian Toyfe, and that of a Pendulum of fe-
    conds, fuch as we have now eflablifht, will be carefully preserved in
    the Magnificent Obfervatory, which His Majefly has caufed to be
    built for the advancement of Aftronomy.
                                                                AR