42 



ASTRONOMY, PROGRESS OP, IN 1893. 



minutes of time, while formerly an hour was 

 necessary. He has also photographed the faculas 

 over the entire disk of the sun, instead of, as 

 previously, near its limb. 



The K line, which is dark in the solar spectrum, 

 is always bright in the faculae, so that a photor 

 graph of the entire sun may be taken by the K 

 light alone ; he having secured such a one with 

 spots, faculae, chromosphere, and prominences 

 all beautifully shown on one plate, and this not 

 a composite photograph, but a monochromatic 

 picture of the sun given by K light only. 



Prof. Kale's achievement in this direction has 

 excited unusual interest among astronomers, and 

 is certainly a great advance in solar physics. 



We are now nearing the middle of the maxi- 

 mum period of sun spots. For scarcely a day 

 during months past nas the sun presented a 

 spotless disk. The rare phenomenon of an 

 equatorial sun spot has been observed, indicative, 

 so considered, of the near approach to maximum 

 of solar activity. See illustration on preceding 

 page, from " Astronomy and Astro-Physics." 



The Moon. The moon will never cease to be 

 an object of telescopic study. Evidence of 

 change long entertained by some astronomers, 

 and strenuously disputed by others, seems to be 

 gradually strengthening, and that the moon is 

 not an absolutely dead world may yet become 

 an article of faith with lunar observers. Pho- 

 tography is constantly bringing to light features 

 hitherto unmapped. Enlargement of the nega- 

 tives of the Lick Observatory reveals the before 

 unknown existence of a crater in the Mare Nu- 

 bium between the southern end of the great 

 "fault," known as the straight wall, and the 

 northwestern side of Pilatus, in size twice as 

 large as any other crater in its vicinity. Still 

 its detection in this manner is not conclusive of 

 change, as, being in a very unattractive neigh- 

 borhood, it might easily have been overlooked. 

 About a half mile eastward the negative reveals 

 a delicate cleft, in shape resembling the Greek 

 letter Zeta (). Prof. Weinck estimates its length 

 to be 5 miles, and its breadth 2 miles. 



Prof. W. H. Pickering, who from his mountain 

 observatory at Arequipa, Peru, has made careful 

 study of the moon, has discovered in the region 

 of Plato reasonably good evidence of actual phys- 

 ical change having taken place within recent 

 times. On the floor of Plato, the spot numbered 

 2, which heretofore has constantly attained in the 

 scale of visibility no higher than 14, now ranks 

 as 5; and No. 25 (No. 40 of Pickering's map), 

 formerly considered as a bright point, is now a 

 crater. He says : " It is perhaps only a coinci- 

 dence, but it may be noted that the 3 craters 

 which seem to have notably increased in size 

 viz., 2, 40, and 47 are all situated very near the 

 edge of the floor, while the 3 which now seem 

 less prominent than formerly 4, 31, and 7 are 

 situated far apart and near the center." 



Prof. Pickering says that No. 4 has never been 

 seen by him as a crater ; but Mr. A. S. Williams 

 saw it as a crater as late as October, 1888. 

 Measurements by Prof. Pickering with a mag- 

 nifying power of 700 on No. 1 gave its diameter 

 as 5,000 feet, and of Nos. 17 and 3 as 4,000 feet. 

 The depth of No. 1, as determined by the length 

 of the shadow cast inside the crater, was found 

 to be 530 feet, assuming the bottom to be flat. 



In the same manner the depths of Nos. 17 and 3 

 were ascertained to be 400 feet each. 



Jupiter. From his mountain observatory, 

 with its unequaled atmosphere, Prof. Picker- 

 ing has with great thoroughness studied the 

 planet Jupiter and his satellites. The best re- 

 sults were secured with a magnifying power of 

 450 diameters on the 13-inch refractor. Under 

 the most favorable atmospheric conditions for 

 seeing, it appeared that the surface of the planet 

 consisted of a uniform white mass of cloud, and 

 that over this, stretched from pole to pole, lay a 

 thin, gauzy veil of unequal density of a brown 

 material not unlike our cirrus clouds. Where 

 it accumulated in dense masses the belts are 

 seen, while the thinner portions formed the 

 spaces between them. Occasionally a round or 

 elliptical hole of 1" to 2" in diameter was seen 

 in this layer. These holes are the well-known 

 white spots observed even with small telescopes. 



The great red spot which, like a floating 

 island having a motion of its own, for a dozen 

 or more years has been, next to the belts, the 

 most striking feature of the planet, was ex- 

 tremely faint, and seen only with great difficulty. 



Jupiter's Satellites. In October, 1892, Prof. 

 Pickering, at Arequipa, Peru, began a series of 

 rigid observations of the four principal satellites 

 of Jupiter, and found the disk of the first satel- 

 lite not circular but egg-shaped. It was un- 

 mistakably thus with powers of 700, 1,000, and 

 2,000. Numerous experiments were tried to dis- 

 cover whether the elongation was not an optical 

 illusion. The next evening he was surprised to 

 view it perfectly round, but later it again as- 

 sumed an oval form. His assistant, Mr. Doug- 

 las, also saw it thus, and several other persons 

 confirmed the observations, which indicated that 

 the satellite, instead of being an oblate spheriod 

 like Jupiter and the other primary planets, was 

 a prolate spheriod whose rotation is accomplished 

 in thirteen hours and three minutes, and which 

 every six hours and thirty minutes became per- 

 fectly circular, remaining thus for half an hour, 

 and the remainder of the time appearing more 

 or less elliptical. Its direction of rotation, Prof. 

 Pickering thinks, is retrograde. 



The other satellites also, though not found 

 spherical, yet instead of revolving end over 

 end, as does the first satellite, were lengthened 

 at right angles to their orbits, like the revolution 

 of a watch if whirling suspended by its chain. 



The third satellite presented an elliptical 

 phase twice during each orbital revolution, at an 

 interval of thirty-four hours after each conjunc- 

 tion with the planet. When this satellite is on 

 the eastern side of its orbit, and presents an 

 elliptical disk, the inclination of the major axis 

 to the orbital plane is clearly shown. On this 

 satellite a peculiar marking has been seen, which 

 at first was thought to be a belt, but further 

 observation indicated for it a more complicated 

 structure, it usually appearing forked, with the 

 prongs at an angle of 30 to 60. The fork 

 turned sometimes to the right and sometimes 

 to the left, and sometimes a double fork was 

 observed like the letter X turned sidewise. To 

 determine the genuineness of this phenomenon 

 of the belt, the eyepiece was changed, the microm- 

 eter and telescope turned, the head of the ob- 

 server held at different angles, and the two 



