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Updated: May 11, 2025
Had cloudy weather intervened, a knowledge of when to look for the object might have greatly facilitated its recognition. It is still an open question, perhaps, whether a great refracting telescope will last unimpaired for an indefinite length of time.
Consequently, the usual method of calculating distance and areas by the eye is ever at fault until custom and familiarity force a new standard of measure. Mirages, too, were of frequent occurrence on the great plains; some of them wonderful examples of the refracting properties of light.
Here the refracting prism or the combination of prisms known as the "spectroscope" comes to its aid, teaching it to measure as well as to perceive. It furnishes, in a word, an accurate scale of colour.
The atmosphere possesses also a reflecting and refracting power, arising from its varying density, and, perhaps, in the latter case, somewhat from its lenticular outline. But for this property we should have no twilight.
Such an objective might, no doubt, be made to conduct any one group of rays of a particular shade to the same focus, but the rays of other colours in the beam of white light must necessarily travel somewhat astray. In this way Newton accounted for a great part of the difficulties which had hitherto beset the attempts to construct a perfect refracting telescope.
Our faculties are limited; and we may be easily deceived, as to what it is that we see with transparent and unerring clearness, and what it is that comes to us through a crooked medium, refracting and distorting the rays of primitive truth. We often seem clear, when in reality the twilight of undistinguishing night has crept fast and far upon us.
At that time Cooke and Clark were the only two men who had ever succeeded in making refracting telescopes of the largest size. But in order to exercise their skill, an art equally rare and difficult had to be perfected, that of the glassmaker. Ordinary glass, even ordinary optical glass, would not answer the purpose at all.
The superstition of later times, acting on and refracting his amazing intellectual gifts, has raised him to a godlike eminence which is by right none of his; it has even credited him with the authorship of Shakespeare, and in its wilder moments with the composition of all that is of supreme worth in Elizabethan literature. It is not necessary to take these delusions seriously.
For this reason work of precision must remain the province of refracting telescopes, although great reflectors retain the primacy in the portraiture of the heavenly bodies, as well as in certain branches of spectroscopy.
The quadrants and circles of Bird, Cary and Ramsden were unapproached abroad. The reflecting telescope came into existence and reached maturity on British soil. The refracting telescope was cured of its inherent vices by British ingenuity.
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