Harriot, Thomas, Mss. 6788

List of thumbnails

< >
851
851 (426r) 		852
852 (426v)
853
853 (427r) 		854
854 (427v)
855
855 (428r) 		856
856 (428v)
857
857 (429r) 		858
858 (429v)
859
859 (430r) 		860
860 (430v)
< >
page |< < (487r) of 1134 > >|
    <echo version="1.0RC">
      <text xml:lang="eng" type="free">
        <div type="section" level="1" n="1">
          <pb file="0973.jpg" o="487r" n="973"/>
          <head xml:space="preserve"/>
          <p>
            <s xml:space="preserve"> or else you may note the altitude as you find it
              <emph style="st">first by</emph>
            by the
              <lb/>
            place of the crosse at first; & after set downe so much
              <emph style="st">as a</emph>
            in degrees
              <lb/>
            or minutes as
              <emph style="st">it is</emph>
            from the place of the crosse answereth to the
              <emph style="st">qua</emph>
            quantity
              <lb/>
            of the excentricity, which hereafter is called the parallaxis of the staffe;
              <lb/>
            to remayne to be abated with some other things as shalbe taught
              <lb/>
            </s>
          </p>
          <p>
            <s xml:space="preserve"> If to the prime end of the staffe that is to say the end which is next the
              <lb/>
            eye nere ioyned a peece of wood of the length of the excentricity the use
              <lb/>
            wold now be somewhat reddier for your owne ey without removing the crosse
              <lb/>
            any otherwise then in the observation, or further consideration of
              <emph style="super">the staffes</emph>
            </s>
          </p>
          <p>
            <s xml:space="preserve"> There is yet an other thing to be noted in observing of altitude by the
              <lb/>
            staffe. The seamen use comonly to leave the horison open
              <emph style="st">the observation</emph>
              <emph style="super">observing</emph>
            ,
              <lb/>
            which in deed were good if they know how much, but because of the uncertayne
              <lb/>
            coniecture they may make greater greater error then is fit to be permitted.
              <lb/>
            They have the practice by tradition from one to the other. The reason thereof they
              <lb/>
            told none in there writings, nether being demanded to they answere
              <lb/>
            any otherwise then that not doing so, the altitude wold not be true, nor
              <lb/>
            agree with the Astrolabe. Which without doubt have ben found by comparing
              <lb/>
            the staffe & the Astrolabe to </s>
          </p>
          <p>
            <s xml:space="preserve"> By truth of demonstration which I have uttered in my Arcticon, which
              <lb/>
            here for brevity sake I omit. I have proved that the ey being above the
              <lb/>
            levell of the water at sea, doth see more then half the heavens. And therefore
              <lb/>
            from the zenith or highest poynt above our heads to the apparent horizon is
              <lb/>
            more then 90 degrees. And that surplus is the greater, according as the
              <lb/>
            ey is above the levell of the water. And therefore any high that is
              <lb/>
            taken by the staffe close, because it hath respecte to the visible horizon, is
              <lb/>
            greater then from the true horizon of the </s>
          </p>
          <p>
            <s xml:space="preserve"> Yet notwithstanding it is the surest way in using the staffe to take the
              <lb/>
            altitude close from the Horizon, because of the uncertayen opening that the
              <lb/>
            Mariners leave. Which altitude without respecte of parallaxis I call
              <lb/>
            the Apparent altitude. And then the surplus with the parallaxis
              <emph style="super">is</emph>
            together
              <lb/>
            are to be abated to make the true altitude </s>
          </p>
          <p>
            <s xml:space="preserve"> The quantity of which surplus I have set downe in a litle speciall
              <lb/>
            table here following according to the sondry distances of the ey from
              <lb/>
            the levell of the </s>
          </p>
          <p>
            <s xml:space="preserve"> As when the ey is one pase that is 5 foote from the levell of the water, then the
              <lb/>
            abatement is
              <math>
                <mstyle>
                  <mn>3</mn>
                  <mo>"</mo>
                </mstyle>
              </math>
            . when 2 pases then
              <math>
                <mstyle>
                  <mn>4</mn>
                  <mo>"</mo>
                </mstyle>
              </math>
            & so forth as in the table.
              <lb/>
            Upon the poope of a tall ship the hight of the ey comonly is 4 or 5 pases &
              <lb/>
            then your abatement is
              <math>
                <mstyle>
                  <mn>5</mn>
                  <mo>"</mo>
                </mstyle>
              </math>
            or
              <math>
                <mstyle>
                  <mn>6</mn>
                  <mo>"</mo>
                </mstyle>
              </math>
            . Upon the decke in the waste
              <math>
                <mstyle>
                  <mn>5</mn>
                  <mo>"</mo>
                </mstyle>
              </math>
            . & at the
              <lb/>
            cheynes
              <math>
                <mstyle>
                  <mn>4</mn>
                  <mo>"</mo>
                </mstyle>
              </math>
            wilbe the abatement, which by triall with the load & line you may
              <lb/>
            </s>
          </p>
          <p>
            <s xml:space="preserve"> And this you ought generally to note that whensoever you observe
              <lb/>
            with the staffe, you make good your high, iust when your ship is
              <lb/>
            on the top of the surge of
              <emph style="super">the</emph>
            sea, otherwise you may </s>
          </p>
        </div>
      </text>
    </echo>
Impressum