6 Biographical Memoir of Sir William Herschel. 



more by peace and the domestic virtues, Herschel, free from all 

 cares, surrounded by a beloved wife and family, devoted to 

 science, surrendered himself to the inspirations of his genius, or, 

 in other words, to an invincible desire of studying nature and 

 interrogating the heavens ; and, to borrow the words of one (4 

 his most celebrated cotemporaries, it was from this solitary vil- 

 lage that the world was instructed in whatever was most singu- 

 lar, and, perhaps, most difficult to perceive in the heavens. 



The history of optical inventions, and of their progressive im- 

 provement, is too well known to require any notice in this place. 

 Herschel's telescopes are those that have been named Newtonian. 

 But he never ceased to study their properties, to vary them, and 

 extend their use. Taught by long experience, he suppressed 

 the plain mirror which produced a second reflection ; and this 

 happy change, wjiich was long before proposed by Lemaire, but 

 difficult of execution, and only applicable in large instruments, 

 doubled, in a manner, the optical effect. 



He found, that, by exercising the eye in a gradual manner, it 

 is rendered much more sensible to the impression of a weak light, 

 and by this means he was enabled to magnify the images of ob- 

 jects much beyond the limits at which other observers had been 

 arrested. He detected two different properties which had not 

 yet been distinguished, that which consists in augmenting the 

 apparent dimension of bodies, and that of penetrating into the 

 profundity of space to discover objects which might have been 

 entirely imperceptible. Multiplied examples leave no doubt re- 

 garding the truth and striking utility of this distinction. 



At length he formed the resolution of carrying the power of 

 these instruments to the highest possible limits ; regarding less 

 the circumstances calculated to facilitate their employment, than 

 those which might augment their optical power, he constructed 

 a telescope of extraordinary dimensions. It is indeed the largest 

 instrument of this kind that has ever been made. 



Let any one imagine to himself an iron tube, 40 feet long and 

 15 inches in diameter, suspended beneath an assemblage of inclin- 

 ed masts, and moved in all directions by a number of machines. 

 The entire system is moveable round a vertical axis, and de- 

 scribes a circumference of 40 feet diameter. A highly polished 

 metallic mirror, weighing about 2000 pounds, is introduced in- 



