The instrument, on its first invention, was generally known by the names of Galileo's tube, the perspective, the double eye-glass: the names of telescope and microscope were suggested by Demisiano, as we are told by Lagalla in his treatise on the Moon.[45]
[33] Histoire des Mathématiques, tom. ii.
[34] "Per duo specilla ocularia si quis perspiciat, altero alteri superposito, majora multo et propinquiora videbit omnia."--Fracast. Homocentrica, § 2, c. 8.
[35] Si utrumque recte componere noveris, et longinqua et proxima majora et clara videbis.--Mag. Nat. lib. 17.
[36] The passage in the original, which is printed alike in the editions of 1598, 1607, 1619, and 1650, is as follows: Visus constituatur centro valentissimus speculi, ubi fiet, et valentissimè universales solares radii disperguntur, et coeunt minimè, sed centro prædicti speculi in illius medio, ubi diametri transversales, omnium ibi concursus. Constituitur hoc modo speculum concavum columnare æquidistantibus lateribus, sed lateri uno obliquo sectionibus illis accomodetur, trianguli vero obtusianguli, vel orthogonii secentur, hinc inde duobus transversalibus lineis, ex-centro eductis. Et confectum erit specillum, ad id, quod diximus utile.
[37] Diximus de Ptolemæi _speculo_, sive _specillo_ potius, quo per sexcentena millia pervenientes naves conspiciebat.
[39] Magia Naturæ et Artis Herbipoli, 1657.
[40] Lettère d'Uomini illustri. Venezia, 1744.
[41] Borelli. De vero Telescopii inventore, 1655.
[42] Encyclopædia Britannica. Art. TELESCOPE.
[45] De phænomenis in orbe Lunæ. Venetiis, 1612.
_Discovery of Jupiter's satellites--Kepler--Sizzi--Astrologers--Mæstlin--Horky--Mayer._
AS soon as Galileo had provided himself with a second instrument, he began a careful examination of the heavenly bodies, and a series of splendid discoveries soon rewarded his diligence. After considering the beautiful appearances which the varied surface of the moon presented to this new instrument, he turned his telescope towards Jupiter, and his attention was soon arrested by the singular position of three small stars, near the body of that planet, which appeared almost in a straight line with it, and in the direction of the ecliptic. The following evening he was surprised to find that two of the three which had been to the eastward of the planet, now appeared on the contrary side, which he could not reconcile with the apparent motion of Jupiter among the fixed stars, as given by the tables. Observing these night after night, he could not fail to remark that they changed their relative positions. A fourth also appeared, and in a short time he could no longer refuse to believe that these small stars were four moons, revolving round Jupiter in the same manner in which our earth is accompanied by its single attendant. In honour of his patron Cosmo, he named them the Medicæan stars. As they are now hardly known by this appellation, his doubts, whether he should call them Medicæan, after Cosmo's family, or Cosmical, from his individual name, are become of less interest.