The tube of this telescope is thirty-nine feet four inches in length, and four feet ten inches in diameter, every part being made of iron. It stands in the open air, appears to be considerably elevated, and is encircled with a complicated scaffolding, by which its steadiness is secured. The concave face of its speculum is forty-eight inches of polished surface in diameter, and it weighs nearly two thousand one hundred and eighteeen pounds! With proper eye-glasses it magnifies above six thousand times: it is the largest instrument, and has the greatest magnifying power, of any that has been made. By its aid, Dr. Herschell has been able to observe the lightning in the atmosphere of the moon, and has found out several celestial bodies, unknown to preceding astronomers. The whole was finished on August the 28th, 1789, on which day the sixth satellite of Saturn was discovered. The observer, suspended at the end of the instrument, with his back towards the object he views, looks down the tube, and sees the image reflected from the mirror; whilst a man below turns gently round the instrument, to accord with the apparent rotatory motion of the heavens, thus preserving the image of the object on the mirror with stability.