_B._ His next words are, “some things are to be considered concerning those variations of the horizontal needle which are not according to the situation of the place from the magnetic poles, but are contrary; as all the West Indies according to the poles should be easterly, and they are westerly. Which is by some accidental cause in the earth; and their motion, as I formerly said, is a forced motion, and not natural.” _A._ He has clearly overthrown his main doctrine. For to say the motion of the needle is forced and unnatural, is a most pitiful shift, and manifestly false, no motion being more constant or less accidental, notwithstanding the variation, to which the inclinatory needle is no less subject than the horizontal needle. _B._ That which deceived him, was, that he thought them two sorts of needles, forgetting what he had said of Norman’s invention of the inclinatory needle by the inclining of the horizontal needle (p. 11). For I will show you that what he says is easterly and should be westerly, should be easterly as it is. Consider the fourth figure, in which B is the north-pole, and B _c_ 11 deg. 15 min. easterly, which was the variation at London in 1576 easterly. Suppose A _c_ to be the needle, shall it not incline, as well here as at D _a_, and the variation B _c_ be easterly? Again, D _a_ is 11 deg. 15 min., and the needle in D parallel to A B, and at _a_ inclining also 11 deg. 15 min. westerly. And is not the variation there D _a_ westerly, with the north point of the needle in the line _a h_? _A._ But the West-Indies are not in this hemisphere B C D E. The variation therefore will proceed in an arc of the opposite hemisphere, which is westerly. _B._ I believe he might think so, forgetting that he and his compass were on the superficies of the earth, and fancying them in the centre at A. _A._ It is like enough. If we had a straight line exactly equal to the arc of a quadrant, I think it would very much facilitate the doctrine of spherical triangles. _B._ When you have done with your questions of natural philosophy, I will give you a clear demonstration of the equality of a straight line to the arc of a quadrant, which, if it satisfy you, you may carry with you, and try thereby if you can find the angle of a spherical triangle given. _A._ It is time now to give over. And at our next meeting I desire your opinion concerning the causes of diaphaniety, and refraction. This Copernicus has done much more than he thought of. For he has not only restored to us astronomy, but also made the way open to physiology. ========== CHAPTER X. OF TRANSPARENCE, REFRACTION, AND OF THE POWER OF THE EARTH TO PRODUCE LIVING CREATURES.