Concerning the first it is but a needlesse labour to recount the diversity of opinions that haue beene held from time to time by learned Geographers. What is the compasse and depth of the earth. This may be seene in _Hues de vsu Globi, part. 3. cap. 2._ and in _Clavius_ on _Sacrobosco_ with others. They all differ so much one from another, that there is no certainty in trusting any of them. The most common and received opinion is that the circuit of the earth is 21600 miles, reckoning 60 miles for every degree, and then the depth or Diameter of the Earth shall be 6877 English miles, containing 5000 foote in a mile. The means wherby the circuit and Diameter of the earth are found out are principally two. 1 By measuring North or South, vnder one Meridian some good quantity of ground, threescore or an hundred miles (or two for the more certainty) for in those petty observations of small distances there can be no certaine working. This may be done, though it be laborious, yet exactly without any sensible error by a skilfull workeman, plotting it out vpon his paper, with due heed taken, that hee often rectifie the variation of the needle (by which he travells) vpon due observation, and that all notable ascents and descents, with such winding and turning as the necessity of the way causeth, be reduced to one streight line. By this means wee shall know how many miles in the Earth answering to a degree in the Heauens; if exact observation by large instruments be made to finde the elevation of the pole, in the first place where wee begin to measure, and the last where wee make an end. Besides this way of measuring the circumference of the Earth, there is none other that hath any certainty of observati[~o] in it. That by Eclipses is most vncertain, for a little error in a few minuts of time (which the observers shall not possibly avoide) breeds a sensible and fowle error in the distance of the two places of observation. That of _Eratosthenes_ by the Sunne beames, and a shadow of a stile or gnomon set vpon the Earth, is as bad as the other. For both the vncertainty of the calculation in so small quantity as the shadow and the gnomon must needs haue, and the difficulty to obserue the true length of the shadow, as also the false supposition wherevpon it proceeds, taking those lines for Paralells which are not, doe manifestly shew the reckoning hereby made to be doubt full and not sure.