One result of the application was a
permanent injury to my sight.
"Wanting some object on which to apply my newly-acquired
mathematical knowledge, I determined to construct an astronomical
telescope. I got Airy's 'Geometrical Optics,' and read it
through. Then I searched through all my English Mechanic (a
scientific paper that I take), and prepared for my work by
reading all the literature on the subject that I could obtain. I
bought two discs of glass, of 6 1/2 inches diameter, and began to
grind them to a spherical curve 12 feet radius. I got them
hollowed out, but failed in fining them through lack of skill.
This occurred six times in succession; but at the seventh time
the polish came up beautifully, with scarcely a scratch upon the
surface. Stopping my work one night, and it being starlight, I
thought I would try the mirror on a star. I had a wooden frame
ready for the purpose, which the carpenter had made for me.
Judge of my surprise and delight when I found that the star disc
enlarged nearly in the same manner from each side of the focal
point, thus making it extremely probable that I had accidentally
hit on a near approach to the parabola in the curve of my mirror.
And such proved to be the case. I have the mirror still, and its
performance is very good indeed.
"I went no further with this mirror, for fear or spoiling it. It
is very slightly grey in the centre, but not sufficiently so as
to materially injure its performance.
Pages:
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452