FOOTNOTES:
[1] Such a telescope is most powerful with the shortest sight. It may be remarked that the use of a telescope often reveals a difference in the sight of the two eyes. In my own case, for instance, I have found that the left eye is very short-sighted, the sight of the right eye being of about the average range. Accordingly with my left eye a 5½-foot object-glass, alone, forms an effective telescope, with which I can see Jupiter's moons quite distinctly, and under favourable circumstances even Saturn's rings. I find that the full moon is too bright to be observed in this way without pain, except at low altitudes.
[2] Betelgeuse—commonly interpreted the Giant's Shoulder—ibt-al-jauza. The words, however, really signify, "the armpit of the central one," Orion being so named because he is divided centrally by the equator.
[3] I have never been able to see more than four with a 3¾-inch aperture. I give a view of the trapezium as seen with an 8-inch equatorial.
[4] Sir W. Herschel several times saw ε Lyræ as a double. Bessel also relates that when he was a lad of thirteen he could see this star double. I think persons having average eye-sight could see it double if they selected a suitable hour for observation. My own eye-sight is not good enough for this, but I can distinctly see this star wedged whenever the line joining the components is inclined about 45° to the horizon, and also when Lyra is near the zenith.
[5] They were so described by Admiral Smyth in 1839. Mr. Main, in 1862, describes them as straw-coloured and reddish, while Mr. Webb, in 1865, saw them pale-yellow and lilac!
[6] Or the observer may sweep from ο towards ν, looking for R about two-fifths of the way from ο to ν.
[7] Here a single period only is taken, to get back to a convenient hour of the evening.
[8] Here a single period only is taken, to get back to a convenient hour of the evening.
[9] I have constructed a zodiac-chart, which will enable the student to mark in the path of a planet, at any season of the year, from the recorded places in the almanacs.
[10] It is convenient to remember that through precession a star near the ecliptic shifts as respects the R.A. and Dec. lines, through an arc of one degree—or nearly twice the moon's diameter—in about 72 years, all other stars through a less arc.
[11] Mercury is best seen when in quadrature to the sun, but not (as I have seen stated) at those quadratures in which he attains his maximum elongation from the sun. This will appear singular, because the maximum elongation is about 27°, the minimum only about 18°. But it happens that in our northern latitudes Mercury is always south of the sun when he attains his maximum elongation, and this fact exercises a more important effect than the mere amount of elongation.
[12] It does not seem to me that the difficulty of detecting Mercury is due to the difficulty "of identifying it amongst the surrounding stars, during the short time that it can be seen" (Hind's 'Introduction to Astronomy'). There are few stars which are comparable with Mercury in brilliancy, when seen under the same light.
[13] I may notice another error sometimes made. It is said that the shadow of a satellite appears elliptical when near the edge of the disc. The shadow is in reality elliptical when thus situated, but appears circular. A moment's consideration will show that this should be so. The part of the disc concealed by a satellite near the limb is also elliptical, but of course appears round.
[14] From a paper by Mr. Breen, in the 'Popular Science Review,' October, 1864.
[15] 'Intellectual Observer' for July, 1867, to which magazine the reader is referred for full details of Mr. Howlett's method of observation, and for illustrations of the appliances he made use of, and of some of his results.
[16] As the sun does not attain such an altitude as 18° during two months in the year, it is well to notice that the true length of the sun's apparent solar diameter is determinable even immediately after sun-rise, if the line of graduation is made to coincide with the horizontal diameter of the picture on the screen—for refraction does not affect the length of this diameter.
[17] The words "Left" and "Right" indicate which end of the sun's ecliptical diameter is uppermost at the dates in upper or lower row respectively.
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