Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 26, 2025
There is no such difficulty with a mirror, because there is in that case no refraction of the light, and consequently no splitting up of the elements of the spectrum. In order to get around the obstacle formed by chromatic aberration it is necessary to make the object glass of a refractor consist of two lenses, each composed of a different kind of glass.
W. R. Dawes with the comparatively small refractor of his observatory at Wateringbury, and on December 3 was described by Mr. Next morning the Times containing the report of Bond's discovery reached Wateringbury. The most surprising circumstance in the matter was that the novel appendage had remained so long unrecognised.
"What's the matter, Tom?" said Uncle Richard one day, as they were busy at work over the telescope, and Tom was scratching his head. "There's nothing the matter, uncle, only I'm a bit puzzled." "What about?" "Over this great glass. It's going to be so different to the old one." "Of course; that is a refractor, and this is going to be a reflector." "Yes, uncle, but it seems so queer.
Still, large telescopes, as a rule, held aloof for some unexplained reason, or were only employed in a desultory and spasmodic fashion, without any very definite object. Birt, the largest instruments available being an 8 1/4 inch reflector and the Crossley refractor of 9 inches aperture!
Frauenhofer, of Munich, took him up in 1805, and soon produced, among others, Struve's Dorpat refractor of 9.9 inches diameter and 13.5 feet focal length, and another, of 12 inches diameter and 18 feet focal length, for Lamont, of Munich. In the nineteenth century gigantic reflectors have been made. Lassel's 2-foot reflector, made by himself, did much good work, and discovered four new satellites.
The Washington 26-inch refractor disclosed to him, under exceptionally favourable conditions, a set of equatorial belts on the disc of Neptune, and they took just the direction prescribed by theory. Their objective reality cannot be doubted, although Barnard was unable, either with the Lick or the Yerkes telescope, to detect any definite markings on this planet.
No other veritable additions of the sun's planetary family have been made in our century, beyond the finding of seven small moons, which chiefly attest the advance in telescopic powers. Of these, the tiny attendants of our Martian neighbor, discovered by Professor Hall with the great Washington refractor, are of greatest interest, because of their small size and extremely rapid flight.
In what follows I have only a refractor in mind, although the same principles would apply to a reflector. With a little practice anybody who has a correct eye can form a fair judgment of the excellence of a telescopic image. Our first object is to see if the optician has given us a good glass.
In some of these ways the lines due to dust might either be avoided or so much reduced in length as not to resemble the true lines of the spectrum. The 15 inch refractor is now being used with a modification of the apparatus employed by Dr. Draper in his first experiments a slit spectroscope from which the slit has been removed.
But this represents only the angle subtended by the star's disk. To learn its linear diameter, we must know its distance. Four determinations of the parallax, which determines the distance, have been made. Elkin, with the Yale heliometer, obtained 0.032 of a second of arc. Schlesinger, from photographs taken with the 30-inch Allegheny refractor, derived 0.016.
Word Of The Day
Others Looking