H4 HISTORY OF THE [1850-60 task in which it proved so efficient that it tended to mislead astronomers into the incautious assumption that, because many nebulae hitherto supposed irresolvable, were supposed to be seen in the field of this powerful instrument separated into their com- ponent stars, given sufficient magnification all nebulae would thus prove to be distant clusters. Lord Rosse was awarded one of the Royal Medals by the Royal Society in 1851, but he never received our Gold Medal, a somewhat curious omission which it is difficult to justify, though the explanation is presumably to be found in the fact that he was pre-eminent not primarily as an observer but rather as an engineer, who developed to a high level of perfection the art of casting, grinding, figuring, and polishing large metal specula and in mounting them for practical observing. Another name which will always be associated with the early use of large reflecting telescopes is that of William Lassell, who had been awarded the Gold Medal in 1849 an d served in the office of President in 1870-72. Lassell was both a constructor and a skilful observer, and not satisfied with our murky skies, he transported his instrument, a reflector of 2-feet aperture and 2O-feet focal length, to Malta in 1852, and observed with it there for some time, replacing it later with an instrument of double the aperture, which he used at Malta in 1862-65. The invention of the silver-on-glass reflector threw the metal mirror out of commission, and a few years ago it might have quite confidently been maintained that no large metal speculum would ever again be undertaken. Lately, when we have seen the almost insuperable difficulties of casting very large glass discs (witness the case of the Mount Wilson zoo-inch, where it took years before a suitable one could be obtained), it is not quite so certain that we or our descendants may not see a reversion to metal. The casting of a metal disc of any desired size presents no insurmountable engineering problems. The last year of our decade saw the most momentous and far- reaching enlargement of the boundaries of astronomy : the applica- tion by Bunsen and Kirchhoff of the principle of spectrum analysis (found by Stokes in 1853) to the determination of the constituents of the solar atmosphere. Kirchhoff 's first paper on this subject was read before the Berlin Academy on 1859 December 15. His full memoir did not appear till eighteen months later, and the early astronomical applications of the new research thus lie within the next decade. We may, however, just note that this announcement, so important to us and marking off so clearly in our estimation the opening of a new epoch, does not seem to have excited very much attention among astronomers at the time. The Astronomer Royal in his suggestions for the observation of the solar eclipse of July 1860, did not allude to the possibility of work of this nature ; nor
