n it absolutely performed. Its merits were after a while
decried, and HERSCHEL even felt obliged to state why he did not always
employ it in his observations. His reasons were perfectly valid, and
such as any one may understand. The time required to get so large a
machine into working order was a serious tax; it required more
assistants than his twenty-foot telescope, and he says, "I have made it
a rule never to employ a larger telescope when a smaller will answer the
purpose."

It still remains as a remarkable feat of engineering and an example of
great optical and mechanical skill. It led the way to the large
reflectors of Lord ROSSE, some sixty years later, and several of the
forty-foot telescopes of the present day even have done less useful
work. Its great feat, however, was to have added two satellites to the
solar system. From the published accounts of it the following is taken:

"When I resided at Bath I had long been acquainted with the theory
of optics and mechanics, and wanted only that experience so
necessary in the practical part of these sciences. This I acquired
by degrees at that place, where in my leisure hours, by way of
amusement, I made several two-foot, five-foot, seven-foot, ten-foot,
and twenty-foot Newtonian telescopes, beside others, of the
Gregorian form, of eight, twelve, and eighteen inches, and two,
three, five, and ten feet focal length. In this way I made not less
than two hundred seven-foot, one hundred and fifty ten-foot, and
about eighty twenty-foot mirrors, not to mention the Gregorian
telescopes.[32]

"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
aerial 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