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The largest siderostat in the world is the Paris 50-inch refractor, which formed the chief attraction of the Palais d'Optique at the Exhibition of 1900. It has a focal length of nearly 200 feet, and can be used either for photographic or for visual purposes.
The Plinius rills form an especially interesting system, and under favourable conditions may be seen in their entirety with a good 4 inch refractor, about the time when the morning terminator passes through Julius Caesar.
G. W. Hough, using the eighteen-and-a-half-inch refractor of the observatory. Inasmuch as these observations are not only of high intrinsic interest, but are in conflict, to some extent, with previous records, a somewhat full abstract of them will be useful: The object of general interest was the great red spot.
It is, assuredly, not an illusory one, since it was plainly apparent, during the opposition of 1886, to MM. Perrotin and Thollon at Nice, and to the former, using the new 30-inch refractor of that observatory, in 1888; Mr.
The same eyepieces will serve for either the reflector or the refractor.
It was finished early in 1868, but at the cost of shortening the life of its maker, who died October 19, 1868, before the giant refractor he had toiled at for five years was completely mounted. This instrument, the fine qualities of which had long been neutralized by an unfavourable situation, was presented by Mr. Newall to the University of Cambridge, a few weeks before his death, April 21, 1889.
Then his views were changed by the revelations due to the great discoveries of Lord Rosse with his gigantic refractor, when one nebula after another was resolved into a cluster of minute stars. At that time the opinion gained ground that with increase of telescopic power this would prove to be the case with all nebulae.
Hence the possibility is not excluded that the star which has an authentic parallax of 0·08" may be visually resolved. Indeed, signs of "elongation" were thought to be perceptible with the Greenwich 28-inch refractor, while only round images could be seen at Lick. Another noteworthy case is that of Polaris, found by Campbell to have certainly one, and probably two obscure attendants.
For procuring both sets of plates, instruments were constructed precisely similar to that of the MM. Henry, which is a photographic refractor, thirteen inches in aperture, and eleven feet focus, attached to a guiding telescope of eleven inches aperture, corrected, of course, for the visual rays.
The 27-inch refractor manufactured by Sir Howard Grubb of Dublin, for the Vienna observatory, a few years ago, was turned on a portion of the moon's disk before being finally sent off to its destination; and seen by the aid of such enormous magnifying power, nothing could be more disappointing as regards the appearance of our satellite.
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