. Galileo, his life and work. nd militarycompass, of which many hundreds were made and sold all overEurope, but on hydrostatic balances, air thermometers, magnets andmagnetic compasses for ships, and various kinds of drawing com-passes Or engineers and architects. He had also added a printing-pres--, where his tract on the Geometrical and Military Compass wasset up. See pp. 43-44 atite. ^ Jupiters satellites, see p. 96 irifra. Galileo continued all these years to grind his own glasses, andit was not until his eyesight began to fail that he consented to 94 PROFESSOR IN PADUA [1592- It detr
. Galileo, his life and work. nd militarycompass, of which many hundreds were made and sold all overEurope, but on hydrostatic balances, air thermometers, magnets andmagnetic compasses for ships, and various kinds of drawing com-passes Or engineers and architects. He had also added a printing-pres--, where his tract on the Geometrical and Military Compass wasset up. See pp. 43-44 atite. ^ Jupiters satellites, see p. 96 irifra. Galileo continued all these years to grind his own glasses, andit was not until his eyesight began to fail that he consented to 94 PROFESSOR IN PADUA [1592- It detracts little from the merit of Galileosinvention that the modern refracting telescope isbased upon a different combination of lenses thanthat which he used. After possessing himself ofone of Galileos instruments, Kepler designed,though he did not make, a telescope consistingof two convex lenses. The difference between thetwo systems can be seen by comparing the adjoin-ing diagram with that of Galileos telescope already Fig. KEPLERIAN TELESCOPE.^ given. Without entering into a detailed description,it may be well to point out that in Galileos therays of light which travel from the point S andpenetrate to the observers eye do not, on strikingthe object-glass, cover the whole of its surface; impart his secret to Ippolito Mariani, commonly known as II Tordo,whom he appointed as his successor in the art. From about 1637,Francesco Fontana of Naples also began to turn out good glasses ofthe Galilean pattern. After Galileos death Torricelli, having devisedan improved way of grinding and polishing lenses, of which he wasthe first to calculate previously the curve, made some instruments ofgreat perfection. Gradually other Italians took up the art, andbecame noted for the excellence of their telescopes, as Viviani,Severino, and Campani. ^ For convenience in drawing the breadth of the telescope isenlarged out of proportion to its length. i6io] KEPLERIAN TELESCOPES 95 and also that (as ex
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