This page has been validated.
of William Herschel.
123
and fifty ten-foot, and about eighty twenty-foot mirrors, not to mention the Gregorian telescopes.[1]
"The number of stands I invented for these telescopes it would not be easy to assign.... In 1781 I began to construct a thirty-foot aërial reflector, and having made a stand for it, I cast the mirror thirty-six inches in diameter. This was cracked in cooling. I cast it a second time, and the furnace I had built in my house broke."Soon after, the Georgian planet was discovered, and this interrupted the work for a time.
"In the year 1783 I finished a very good twenty-foot reflector with a large aperture, and mounted it upon the plan of my present telescope. After two years' observation with it, the great advantage of such apertures appeared so clearly to me that I recurred to my former intention of increasing them still further; and being now sufficiently provided with experience in the work which I wished to undertake, the President of the Royal Society, who is always ready to promote useful undertakings, had the goodness to lay my design before the king. His Majesty was graciously pleased to approve of it, and with his usual liberality to support it with his royal bounty.
- ↑ At least one of these telescopes had the principal mirror made of glass instead of metal.—Philosophical Transactions, 1803.
