motes in the beam of their primary—itself an atom to our sight, noticed only by the careless vulgar as a large star, and by the philosophers of former ages as something moving among the stars, they knew not what, nor why: perhaps only to perplex the wise with fruitless conjectures, and harass the weak with fears as idle as their theories."[55] FOOTNOTES: [46] Venturi. Essai sur les ouvrages de Leo. da Vinci. [47] Dianoia Astronomica, Venetiis, 1610. [48] Kepleri Epistolæ. [49] Kepleri Epistolæ. [50] It may seem extraordinary that any one could support an argument by this partial disbelief in the instrument, which was allowed on all hands to represent terrestrial objects correctly. A similar instance of obstinacy, in an almost identical case though in a more unpretending station, once came under the writer's own observation. A farmer in Cambridgeshire, who had acquired some confused notions of the use of the quadrant, consulted him on a new method of determining the distances and magnitudes of the sun and moon, which he declared were far different from the quantities usually assigned to them. After a little conversation, the root of his error, certainly sufficiently gross, appeared to be that he had confounded the angular measure of a degree, with 69½ miles, the linear measure of a degree on the earth's surface. As a short way of showing his mistake, he was desired to determine, in the same manner, the height of his barn which stood about 30 yards distant; he lifted the quadrant to his eye, but perceiving, probably, the monstrous size to which his principles were forcing him, he said, "Oh, Sir, the quadrant's only true for the sky." He must have been an objector of this kind, who said to Galileo,—"Oh, Sir, the telescope's only true for the earth." [51] Venturi. [52] Quatuor probl. confut. per J. Wedderbornium, Scotobritannum. Patavii, 1610. [53] See page 18. [54] Sherburne's Sphere of Manilius. London, 1675. [55] Herschel's Address to the Astronomical Society, 1827. CHAPTER VIII. _Observations on the Moon—Nebulæ—Saturn—Venus—Mars._