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The light, after passing through the lenses, is brought to a focus at the lower end of the tube, where the image is examined visually with an eyepiece, or photographed upon a sensitive plate. The largest instruments of this type are the 36-inch Lick telescope and the 40-inch refractor of the Yerkes Observatory.
Duly apprised of the recurrence of a phenomenon he had himself vainly looked for during some years, M. von Konkoly took the opportunity of the great Vienna refractor being placed at his disposal to examine with it the relighted spectrum on August 27.
In addition to the crater just mentioned, there are two smaller ones below the summit of the S. wall, and a small circular depression on the S.E. wall. Mr. W.H. Maw, F.R.A.S., has seen, with a 6 inch Cooke refractor, a bright marking at the N. extremity of the ring, which, when examined with a Dawes' eyepiece, resembled an imperfect crater.
Thirty-two Wolf-Rayet stars were investigated, spectroscopically and spectrographically, by Professor Campbell with the great Lick refractor in 1892-94; and several disclosed the singularity, already noticed by him in Gamma Argûs, of giving out mixed series, the members of which change from vivid to obscure with increase of refrangibility.
The latter hypothesis seems the more probable: and its probability is strengthened by much evidence of actual obscuration or variation of tint in other parts of the lunar surface, more especially on the floor of the great "walled plain" named "Plato." From a re-examination with a 13-inch refractor at Arequipa in 1891-92, of this region, and of the Mare Serenitatis, Mr.
The exquisite little picture of Saturn was taken at Paris by MM. Paul and Prosper Henry, December 21, 1885, with their 13-inch photographic refractor. The telescopic image was in this case magnified eleven times previous to being photographed, an exposure of about five seconds being allowed; and the total enlargement, as it now appears, is nineteen times.
De Vico's accounts of it appear to me to have not a little of the extra-marvellous in them. And all by a Cauchoix refractor of eight inches? I fear me that these wonders are not for female eyes, the good monks are too well aware of the penetrating qualities of such optics to allow them entry within the seven-fold walls of their Collegio. Has Somerville ever looked through it?
Not only did it appear greatly extended in the Vienna 27-inch, but MM. Perrotin and Thollon saw it with the Nice 15-inch, and M. Kammermann of Geneva, employing special precautions, with a refractor of only ten inches aperture.
The superiority of the refractor in regard to definition arises from the fact that any distortion at the surface of a mirror affects the direction of a ray of light three times as much as the same distortion would do at the surface of a lens. And this applies equally both to permanent errors of curvature and to temporary distortions produced by strains and by inequality of temperature.
'Let me collect myself; he is going to the observatory of Cambridge, United States, to meet some gentlemen there, and spy through the great refractor.
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