[8] This was probably due not only to unfavorable climate, but to the fact that Herschel, with all his ingenuity, does not appear to have mastered the casting difficulty, and was constrained to make his big speculum of Cu 75 per cent, Sn 25 per cent, a composition working rather easily and taking beautiful, but far from permanent, polish. He never seems to have used practically the SnCu_{4} formula, devised empirically by Mudge (Phil. Trans. _67_, 298), and in quite general use thereafter up to the present time. [Illustration: FIG. 20.—Herschel’s Front View Telescope.] It was used as a front view instrument and was arranged as shown in Fig. 21. Obviously the front view form has against it the mechanical difficulty of supporting the observer up to quite the full focal length of the instrument in air, a difficulty vastly increased were the mount an equatorial one, so that for the great modern reflectors the Cassegrain form, looked into axially upward, and in length only a third or a quarter of the principal focus, is almost universal. As soon as the excellent results obtained by Herschel became generally known, a large demand arose for his telescopes, which he filled in so far as he could spare the time from his regular work, and not the least of his services to science was the distribution of telescopes of high quality and consequent strong stimulus to general interest in astronomy. Two of his instruments, of 4-and 7-feet focus respectively, fell into the worthy hands of Schröter at Lilienthal and did sterling service in making his great systematic study of the lunar surface. At the start even Herschel’s 7-foot telescope brought 200 guineas, and the funds thus won he promptly turned to research. [Illustration: _Miss Clerke’s Herschel & Modern Astronomy_ (_Macmillan_). FIG. 21.—Herschel’s Forty-foot Telescope.] We sometimes think of the late eighteenth century as a time of license unbounded and the higher life contemned, but Herschel wakened a general interest in unapplied science that has hardly since been equalled and never surpassed. Try to picture social and official Washington rushing to do honor to some astronomer who by luck had found the trans-Neptunian planet; the diplomatic corps crowding his doors, and his very way to the Naval Observatory blocked by the limousines of the curious and admiring, and some idea may be gained of what really happened to the unassuming music master from Bath who suddenly found himself famous. Great as were the advances made by Herschel the reflector was destined to fall into disuse for many years. The fact was that the specula had to be refigured, as in the case of the great 40-foot telescope, quite too often to meet the requirements of the ordinary user, professional or amateur. Only those capable of doing their own figuring could keep their instruments conveniently in service.