Biographical Memoir of Sir William Herschel. 211 
ledge of mathematics, while residing at Halifax ; but the doe- 
trines of astronomy had, in an especial manner, fixed his atten- 
tion, and while he studied, in the popular writings of Ferguson, 
the wonders of the planetary system, as disclosed by the tele- 
scope, he was actuated by the most vehement desire of witness- 
ing, with his own eyes, such remarkable phenomena. The 
price of a telescope capable of exhibiting the most interesting of 
the planetary phenomena, was, luckily for science, far beyond 
the means of Mr Herschel ; but his zeal was not to be damped 
by a difficulty of this nature, and he resolved to construct a te- 
lescope with his own hands. After encountering and over- 
coming the difficulties which every amateur must have expe- 
rienced in the formation of reflecting telescopes, he completed, 
in 1774, a five feet reflector, with which he observed the ring of 
Saturn, and the satellites of J upiter. “ When I resided at Bath,™ 
says Dr Herschel, “ I had long been acquainted with the 
theory of optics and mechanics, and wanted only that experience 
which is 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 for myself several 2-feet, 5-feet, 
7-feet, 10-feet, and 20-feet Newtonian Telescopes, besides others 
of the Gregorian form, of 8 inches, 12 inches, 2 feet, S feet, 5 
feet, and 10 feet focal length. My way of doing these instru- 
ments at that time, when the direct method of giving the figure 
of any one of the conic sections to specula was still unknown to 
me, was to have many mirrors of each sort cast, and to finish 
them all as well as I could, then to select by trial the best of 
them, which I preserved ; the rest were put by to be repolish- 
ed. In this manner I made not less than 200 7-feet, 150 10- 
feet, and about 80 20-feet, not to mention those of the Grego- 
rian form, or of the construction of Dr Smith’s reflecting mi- 
croscope, of which I also made a great number. My mechani- 
cal amusements went hand in hand with the optical ones. The 
number of stands I invented for those telescopes it would not 
be easy to assign. I contrived and delineated them of different 
forms, and executed the most promising of the designs. To 
those labours we owe my 7-feet Newtonian telescope stand, 
which was brought to its present convenient construction about 
1778.”— PM, Trans . 1795. p. 347. 
