62 



ASTKONOMICAL PHENOMENA AND PKOGRESS, 



about the time of perihelion, in the latter part 

 of January. From Nov. 27, 1883, to March 

 3, 1S84, the comet was reported visible to the 

 naked eye. The tail, which was detected about 

 the first of December, attained a length of 

 six by January 20, and then faded out grad- 

 ually until it was invisible even in the telescope 

 >ruary 26. The nucleus was observed 

 as late as March 29, 188-4. The spectroscope 

 gave the usual hydrocarbon spectrum of 

 comets. 



The second comet of 1884, in order of peri- 

 helion passage as well as of discovery, was 

 found by Barnard, at Nashville, Tenn., July 16, 

 1884. It was a nebulous object, slightly con- 

 densed near the center, and, for a telescopic 

 comet, quite bright. The orbit proved to be 

 elliptical, with a period of about 5 years, peri- 

 helion occurring August 16. The elements 

 bear a remarkably close resemblance to those 

 of De Vice's comet of 1844 (1844 I), but the 

 identity of the two objects is improbable. The 

 comet, at no time prominent, was last reported 

 visible about the end of October. 



A new comet was discovered by Wolf, a 

 student of astronomy at Heidelberg, on Sept. 

 17, 1884. It appears to belong to the group 

 of the Faye-Moller comet (comet 1857 IV, 

 and comet 1874 IV). There is no evidence of 

 any previous appearance, though, if the pe- 

 riod of 6 - 75 years assigned is correct, it would 

 be visible from the earth at only about every 

 third return. The comet shows a pretty well- 

 defined, star-like nucleus surrounded by its 

 nebulous envelope, but it has not developed a 

 tail. Perihelion was passed Nov. 17, 1884. 

 The fact that this comet was never before ob- 

 served, although it is now moving in an orbit 

 in which the time of revolution is less than 

 seven years, led Dr. Krueger to investigate 

 the question whether we had not another case 

 of a comet taking a new orbit by the action 

 of Jupiter. Tracing back the course of the 

 comet, lie found that about May 28, 1875, it 

 must have passed very near to Jupiter, and 

 might therefore have had its orbit entirely 

 changed. Another astronomer has undertaken 

 to compute the change produced in the orbit 

 by tliis approach, and found that before 1875 

 it might have been moving in a much larger 

 orbit. This result is, however, entirely uncer- 

 tain, owing to the want of exact knowledge of 

 the time of revolution. All that can be said 

 with confidence is that a great change was 

 produced by the action of Jupiter. It will 

 probably perform seven or nine revolutions in 

 IN jnvsent orbit without again approaching 

 Jupiter, and may then again encounter that 

 planet and be once more thrown into a new 

 orbit. 



A round, faint, nebulous object was found 

 by Spitaler on the evening of May 26, 1884, 

 while he was searching with the twenty-seven- 

 inch refractor of the Vienna Observatory for 

 comet 1858 III. Unfavorable weather pre- 

 vented a re-examination of this part of the sky 



till June 17 and 18, and then the object could 

 no longer be seen ; nor could it be found after- 

 ward. It is still doubtful whether this was the 

 expected comet of 1858 or not. 



Pickering's Photometric Researches. The appli- 

 cation of the photometer to astronomical re- 

 search has been a specialty of the Harvard 

 Observatory since Prof. Pickering became 

 its director. The method of observing the 

 eclipses of Jupiter's satellites by the photom- 

 eter is likely to be a great improvement in 

 accuracy upon the older eye-methods, and may 

 be expected to supersede them for all the pur- 

 poses of accurate astronomy. The greatest 

 work of this class is the determination of the 

 brilliancy of all the stars down to the sixth 

 magnitude visible at Cambridge by means of 

 a meridian photometer. The latter is an in- 

 strument of Prof. Pickering's invention. It is 

 so arranged that an image of the pole-star is 

 always visible in the field of view, and is used 

 as a standard of comparison. The instrument 

 itself is mounted in an east-and-west horizontal 

 position. It has two objectives of the same 

 aperture and focal length. A prism in front of 

 each reflects the light of a star, the one being 

 used for the pole-star, and the other for the star 

 to be measured. The latter prism may be 

 turned round the axis of the telescope, so as to 

 form an image of any star sufficiently near the 

 meridian. The two pencils as they leave the 

 object-glass are each divided by a double re- 

 fracting prism, in such a way that one ray from 

 each is made to coincide. The result of many 

 ingenious devices and precautions is, that the 

 images of the two stars can be brought into 

 close juxtaposition, and by means of a polariz- 

 ing apparatus the two images can be brought 

 into exactly equal brilliancy. The observations 

 occupied the four years, 1879 to 1882, and the 

 results, as published in Volume XVI of the 

 " Harvard Observatory Annals," form one of 

 the most available catalogues of the bright- 

 ness of stars now at the command of astron- 

 omers. 



Astronomical Photography. In Dr. Gill's photo- 

 graphs of the great comet of 1882. taken at the 

 Cape of Good Hope Observatory, it was found 

 that the stars down to the eighth and ninth 

 magnitude were clearly depicted on the plate. 

 This fact suggested a new method of forming 

 approximate catalogues of the fainter stars by 

 taking photographs of regions of the heavens, 

 several degrees square, and afterward meas- 

 uring the position of the stars on the plates. 

 The method has been tried at the Harvard 

 College Observatory by Mr. W. H. Pickering. 

 He had in view the construction of a photo- 

 graphic map of the whole heavens, and the 

 determination of the light of the brighter stars. 

 He succeeded in obtaining maps nearly 15 

 square, containing stars as faint as the eighth 

 magnitude. Should the method prove a suc- 

 cess, it is expected that catalogues of the faint- 

 er stars can be made with far less labor than 

 heretofore. 



