Description of a Forty-Feet Reflecting Telescope.

HERSCHEL, William

Verlag: J. Nichols

Beschreibung

THE VERY RARE SEPARATELY PAGINATED OFFPRINT FROM THE PHILOSOPHICAL TRANSACTIONS OF HERSCHEL'S DESCRIPTION OF HIS FAMOUS TELESCOPE. [Herschel] seems quickly to have realized that in order to investigate very distant (and therefore faint) objects, he would need telescopes with considerable light-gathering power, for a telescope directed to a faint object must not only magnify it but also collect enough light for the magnified image to be visible to the observer. As he put it in 1800, light-gathering power is "the power of penetrating into space." His need was therefore for reflectors with large mirrors; and as his ambitions grew, he found himself forced to undertake an increasing share of the labor of construction himself. In the grinding and polishing of large mirrors, and in the working of exquisite eyepieces, Herschel was soon without peer; and when in 1782 one of his telescopes was taken to the Royal Observatory for comparison with the instruments there, Nevil Maskelyne, the astronomer royal, conceded superiority to Herschel. For the rest of his life Herschel enjoyed the possession of telescopes which were incomparably the most powerful of the period for the study of faint objects, although he never attempted the carefully mounted and graduated instruments required for exact positional astronomy. In 1785 Herschel successfully requested the king to finance a fresh attempt to build a large telescope. "It remained now only to fix upon the size of it, and having proposed to the King either a 30 or a 40 feet telescope, His Majesty fixed upon the largest." Four years of labor followed for Herschel and his team of workmen, during which the original grant of £2,000 was doubled and an annual allowance of £200 was also made. The mirrors of forty-eight-inch diameter were cast in London, but all other work was carried out at Slough under Herschel s direction. In mounting the mirror in the tube Herschel tilted it slightly to one side so that the observer might peer through the eyepiece directly at the mirror, without the need for additional mirrors (the "Herschelian" arrangement). The monster telescope was completed in 1789 and immediately revealed a sixth satellite of Saturn. But it was never fully satisfactory: the mirrors tarnished quickly, the structure was cumbersome to turn, and when Herschel in 1790 altered his opinion of the nature of nebulae, he thereby answered the very question of the telescope s great light-gathering power may have been intended to settle. Yet it became one of the wonders of the world and a visible testimony to Herschel s mechanical ingenuity and to the scale of his cosmological ambitions (DSB). Bestandsnummer des Verkäufers 3d6043b8d3fb1655c83e95f529991b93

Bibliografische Details

Titel: Description of a Forty-Feet Reflecting ...

Verlag: J. Nichols

Einband: Hardcover

Zustand: Excellent