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Astronomical Society of the Pacific.
VOL. III. SAN FRANCISCO, CALIFORNIA, JANUARY 31, 1891.
OBSERVATIONS AND DRAWINGS OF SATURN, 1879-1889.*
BY EDWARD S. HOLDEN.
During the years 1879-1890, I have made many observations of Saturn with the 26-inch equatorial at Washington (1879-80), the 15inch at the Washington Observatory (1881-85) and with the 36-inch at the Lick Observatory (1888-90).
For the purpose of recording my notes graphically, I had a set of blank forms engraved on wood, so that the set of six forms would represent (approximately) every degree of inclination of Saturn's ring. Each of the accompanying sketches is made on one of these forms; and some distortion of the true figure is introduced in this way. Only that part of each sketch was finished which seemed to have some special significance at the time of observation. The drawings were not intended to be completed pictures, but graphic notes to accompany the written memoranda herewith.
The scale of shading has not been kept constant throughout the eleven years. Two surfaces, equally dark in the accompanying sketches, might have been of quite different brightness when seen on the planet. In the blank forms the engraver inserted some bounding lines, which should have been omitted. Where these are especially misleading I have inserted an x in the foregoing sketches. In spite of these various faults, I have thought that the sketches, and particularly the notes of observation, might be worthy of publication, and I beg to present them to the Society. The planet has been observed on very many occasions of which there is no note here, without seeing any feature calling for special remark.
* See frontispiece. The Lithographer has been unable to copy my original drawings and I have changed them somewhat by retouching, making them far less satisfactory to myself in the
The observations were all made with unusually powerful telescopes. A particular feature in regard to the series is that the sketches do not show certain peculiarities of Saturn, which have been reported by other observers with smaller telescopes. This may be due to a failure on my own part, but I am inclined to think that it is sometimes, at least, due to the fact that the phenomena of the very complex system of Saturn are often too difficult for small instruments. A feature which, by its small size, or by its faintness, is at or near the limit of vision for a small telescope, can often be seen with perfect precision in a larger one. The shortcomings in the present notes cannot, at any rate, be attributed to the instruments employed, since they have all been proved to be of first-class excellence.
The drawings are arranged so that the N. pole of Saturn is towards the bottom of the figure, and the W. end of the ring is towards the left hand. The outer ring is called A, the main ring B, the dusky ring C. The principal division between A and B is the CASSINI division. The division in ring A (before 1888) is the ENCKE division. No division was seen between rings B and C during these observations.
The steadiness of the atmosphere is noted on a scale of 5 perfectly steady, 3 average, I extremely unsteady. Notes added in copying for publication have been put in brackets [ ].
Notes of Observations of Saturn.
1879, Sept. 24,
12h W. m. t. 26-inch equatorial. Wt. 2. (See Figure 1.) The CASSINI division can be traced no further than it is drawn in the figure. The shadow of the ball on the ring is not black, but ashy-grey; it is not more than o".5 wide at its north end, nor more than 1.5 at its south end, and it appears convex to the ball.
1879, Sept. 29.
About 11 W. m. t. 26-inch equatorial. Wt. 4. (See Figure 2). The CASSINI division is as drawn. The division in Ring A is seen at the west end only. Ring B consists of two main parts; the outer part is bright, the inner is grey and much fainter.
1879, Oct. 11, 12" 15" W. m. t. 26-inch equatorial. Wt. 5. (See Figure 3). The original drawing is a sketch of the shadows only. Nothing is said about the CASSINI division in front of the ball. Shadows of the ball on the ring are visible on both sides of Saturn.