This virtually new engine of research was delivered and mounted in 1829, three years after the termination of the life of its deviser. The Dorpat lens had brought to Fraunhofer a title of nobility and the sole management of the Munich Optical Institute (completely separated since 1814 from the mechanical department). What he had achieved, however, was but a small part of what he meant to achieve. He saw before him the possibility of nearly quadrupling the light-gathering capacity of the great achromatic acquired by Struve; he meditated improvements in reflectors as important as those he had already effected in refractors; and was besides eagerly occupied with investigations into the nature of light, the momentous character of which we shall by-and-by have an opportunity of estimating. But his health was impaired, it is said, from the weakening effects of his early accident, combined with excessive and unwholesome toil, and, still hoping for its restoration from a projected journey to Italy, he died of consumption, June 7, 1826, aged thirty-nine years. His tomb in Munich bears the concise eulogy, _Approximavit sidera_.
Bessel had no sooner made himself acquainted with the exquisite defining powers of the Königsberg heliometer, than he resolved to employ them in an attack upon the now secular problem of star-distances. But it was not until 1837 that he found leisure to pursue the inquiry. In choosing his test-star he adopted a new principle. It had hitherto been assumed that our nearest neighbours in space must be found among the brightest ornaments of our skies. The knowledge of stellar proper motions afforded by the critical comparison of recent with earlier star-places, suggested a different criterion of distance. It is impossible to escape from the conclusion that the apparently swiftest-moving stars are, _on the whole_, also the nearest to us, however numerous the individual exceptions to the rule. Now, as early as 1792,[69] Piazzi had noted as an indication of relative vicinity to the earth, the unusually large proper motion (5·2" annually) of a double star of the fifth magnitude in the constellation of the Swan. Still more emphatically in 1812[70] Bessel drew the attention of astronomers to the fact, and 61 Cygni became known as the "flying star." The _seeming_ rate of its flight, indeed, is of so leisurely a kind, that in a thousand years it will have shifted its place by less than 3-1/2 lunar diameters, and that a quarter of a million would be required to carry it round the entire circuit of the visible heavens. Nevertheless, it has few rivals in rapidity of movement, the apparent displacement of the vast majority of stars being, by comparison, almost insensible.