If the dates given by Simon Marius in his _Mundus Jovialis_ be correct, a Belgian with an air of mystery and a glass of which one of the lenses was cracked, turned up at the Frankfort fair in the autumn of 1608 and at last allowed Fuchs, a nobleman of Bimbach, to look through the instrument. Fuchs noted that it magnified “several” times, but fell out with the Belgian over the price, and returning, took up the matter with Marius, fathomed the construction, tried it with glasses from spectacles, attempted to get a convex lens of longer focus from a Nuremburg maker, who had no suitable tools, and the following summer got a fairly good glass from Belgium where such were already becoming common. With this Marius eventually picked up three satellites of Jupiter—the fourth awaited the arrival of a superior telescope from Venice. Early in 1609 telescopes “about a foot long” were certainly for sale in Paris, a Frenchman had offered one in Milan by May of that year, a couple of months later one was in use by Harriot in England, an example had reached Cardinal Borghese, and specimens are said to have reached Padua. Fig. 2 from the “_Mundus Jovialis_,” shows Marius with his “Perspicilium,” the first published picture of the new instrument. Early in 1610 telescopes were being made in England, but if the few reports of performance, even at this date, are trustworthy, the “Dutch trunk” of that period was of very indifferent quality and power, far from being an astronomical instrument. [Illustration: _The Observatory._ FIG. 2.—Simon Marius and his Telescope.] One cannot lay aside this preliminary phase of the evolution of the telescope without reference to the alleged descriptions of telescopic apparatus by Roger Bacon, (c. 1270), Giambattista della Porta (1558), and Leonard Digges (1571), details of which may be found in Grant’s _History of Physical Astronomy_ and many other works. Of these the first on careful reading conveys strongly the conviction that the author had a pretty clear idea of refraction from the standpoint of visual angle, yet without giving any evidence of practical acquaintance with actual apparatus for doing the things which he suggests. Given a suitable supply of lenses, it is reasonably certain that Bacon was clever enough to have devised both telescope and microscope, but there is no evidence that he did so, although his manifold activities kept him constantly in public view. It does not seem unlikely, however, that his suggestions in manuscripts, quite available at the time, may have led to the contemporaneous invention of spectacles. Porta’s comments sound like an echo of Bacon’s, plus a rather muddled attempt to imagine the corresponding apparatus. Kepler, certainly competent and familiar with the principles of the telescope, found his description entirely unintelligible. Porta, however, was one of the earliest workers on the _camera obscura_ and upon this some of his cryptic statements may have borne.