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On the east side the principal division (prolonged) plainly intersects the ball. On the west side, however, it is almost tangent to it.
A kind of reason for this can be given. On the east side the outer ellipse of Ring A comes close to the ball with no black division in between them. It, therefore, seems tangent to it. On the W. side first comes the south limb of the ball, then the shadow of the ball on the ring and beyond and south of this is the Ring A. A very little change in the correct appreciation of the angle terminating the shadow will alter the position of the end of the Ring A greatly. The illusion in regard to the prolongation of the principal division I explain by supposing the eye makes this ellipse to be similar to that of the outer ellipse of Ring A, and does not takes its true shape as a guide.
1882, Oct. 3. 151⁄2-inch equatorial, Eye-piece 145. (See Figure 17 a.)
The general shape of the shadow of the ball on the ring is as drawn, only I have exaggerated the dimensions in
order to show the true form more clearly.
ball and of the ring are about tangent. north of the ring.
The south limbs of the None of the ball is visible
1882, Nov. 8. 151⁄2-inch equatorial, Eye-pieces 145, 240.
The north pole of the ball is just barely visi
(See Figure 18.) ble north of the ring. The principal division is seen all around. The night is very fine. The ENCKE division in Ring A is well seen on the west side as far as the end of the major axis of the dusky ring (outer ellipse.) It is not so well seen on the east side. It divides Ring A into two parts as 2 to 3. [It is, therefore, of the way from the outer ellipse of Ring A towards the inner one.] The southern hemisphere of the ball is dark; the region near the south pole is the darkest. There is a dark stripe along the south edge of the bright equatorial belt, and this belt has a narrow stripe along its middle. The shadow of the ball on the ring is seen on both sides of the ball, and the shape is the same on both sides, but the shadow on the west is darker than that on the east.
1883, Nov. 24.
151⁄2-inch equatorial, Eye-piece 145.
(See Figure 19.) The ENCKE division is not seen. The CASSINI division is seen all around. The drawing is made to show the shape of the shadow of the ball on the rings. The principal division forms a part of this, and the south limb of the ball of the planet looks like a straight line.
151⁄2-inch equatorial, Eye-piece 195.
1883, Dec. 2. (See Figure 20.) The CASSINI division is seen all around. The ENCKE division is seen at both ends of the ring. The shadow of the ball of the ring is as drawn. It is wider and of a different shape at the west end, as drawn. I did not specially look for (nor see) the shadow of the ball on the Ring C. The south polar region of the ball of the planet is mottled, especially near the shadows. The bright equatorial belt is bounded on the south by a narrow, dark streak some 2" wide. This is the darkest marking on the ball. South of this is an equally narrow, bright streak, and south of this again is the nearly uniform southern hemisphere. North of the equatorial bright belt is a narrow, dusky belt (11⁄2"?), then a narrow, bright belt (11⁄2" ?), and then a dark band, which is the dusky ring itself (Ring C).
1888, Nov. 5. 36-inch equatorial, Eye-piece 600. Observers, J. M. SCHAEBERLE and E. S. HOLDEN.
(Drawing omitted.) The southern hemisphere is olive-green.
[The south polar region itself is the same color over a region about o".5 (north and south) by 2".2 (east and west). This region is enclosed by a narrow, dark belt (first discovered by J. M. S., which is a little less than 1" in width.]
1889, March 22, 8h 30m P. s. t. 36-inch equatorial, Eye-piece 2000, Wt. 5. Slight haze. Observers J. M. S. and E. S. H. (See Figure 21.) KEELER'S division is seen. J. M. S. sees a new division in Ring B, as drawn. [It was estimated as 1/4 of the width of Ring B from its inner ellipse, but the sketch made does not agree with this. The existence of this division has never been confirmed].
Beside the foregoing unpublished observations, the following publications relating to the appearance of the planet have been made by one or more of the astronomers of the Lick Observatory:
Saturn and his Satellites, Sidereal Messenger for January, 1889. Reported Changes in the Rings of Saturn, Astronomical Journal, vol. 8, page 180.
The Square-shouldered Aspect of Saturn, Publications A. S. P., July 12, 1890.
First Observations of Saturn with the 36-inch Equatorial, Sidereal Messenger, 1888, page 79.
The Appearance of Saturn in the 36-inch Telescope, Ciel et Terre, January, 1889, page 514.
The Outer Ring of Saturn, Ciel et Terre, April, 1889.
INDEX-MAP OF THE MOON.*
[BY PROFESSOR CHARLES A. YOUNG, Director of the Halstead Observatory, Princeton, N. J.]
"The accompanying figure is reduced from a skeleton map of the moon, by NEISON, and though not large enough to exhibit much detail, will enable a student, with a small telescope, to identify the principal objects by the help of the key."
KEY TO THE PRINCIPAL OBJECTS INDICATED ON THE INDEX-MAP.
* We owe to the kind permission of Professor YOUNG, and of his publishers, the right to re
print the following from his Elements of Astronomy, 1890.
In consequence of a growing need felt in the teaching of Astronomy here at Swarthmore College, for some suitable apparatus for
illustrating the methods of finding Latitude, Time, etc., it was determined, about five years ago, to make an effort to secure a small observatory equipped with instruments for teaching purposes. It was thought that, perhaps, a sum of $2000 would cover the cost of the necessary apparatus, and suitably house it; in consequence of this, a committee from the Board of Managers of the College was appointed to see what might be done in the way of obtaining subscriptions to the enterprise. The result was that a sum of about
$7000 was obtained, with which a neat building was constructed of wood, containing a central dome, in which is placed the equatorial telescope; and the two wings, one for the transit instrument and mean-time clock, and the other for a work-room. The latter has been suitably warmed from the professor's house adjoining; in this room the nucleus of a library is placed with the batteries, chronograph and chronometer. On the ground floor of the central building is placed the sidereal clock.
In the dome stands a six-inch refractor, with object-glass by ALVAN CLARK & SONS, and mounting by WARNER & SWASEY; it is provided with clock-work, and an attachment for the electrical illumination of the circles and micrometer. There are five eye-pieces, varying in power from 75 to 500, a large eye-piece for the moon, and a diagonal eye-piece for both sun and stars, and also a microThere is also a very fine spectroscope, with a ROWLAND. grating, constructed by BRASHEAR, but no photographic apparatus.
The transit instrument with 31⁄2-inch object-glass is also of WARNER & SWASEY's mounting, and stands upon a foundation of solid mason work of about twelve feet in depth; it is provided with two large finding circles, one roughly graduated, and the other graduated upon silver to 10" of arc, and carrying two verniers, a striding level, and also a level attached to the horizontal axis of the telescope; to the eye-piece is attached a micrometer, capable of being turned onequarter around, in order that, with the second level, the instrument may be used as a zenith telescope, as well as a transit instrument. The chronograph is also of WARNER & SWASEY'S make, and can be connected with either clock. A barometer, wet and dry bulb thermometers, also a maximum and minimum thermometer, made by H. J. GREEN, of New York, were added about two years ago, and observations are recorded three times daily, in connection with the Pennsylvania State Weather Service (the observatory being a volunteer station.) A rain-gauge and anemometer, with registering clock, are also among the meteorological outfit, and during the present year a DRAPER's self-registering thermometer has been added. The U. S. Signal Service weather flags are displayed daily, according to the data announced by the service, and a weather map is received and placed on view each day.
As yet the observatory, according to its original design, has been used for teaching purposes only, and for the pleasure of visitors, but it is hoped that, in time, astronomical work may be done here.