ASTRONOMICAL PHENOMENA AND PROGRESS. 



53 



Possible Influence of Cosmical Dnst. The phe- 

 nomena of meteors and shooting-stars show that 

 matter is constantly falling upon the earth from 

 space. But science has hitherto furnished no 

 method of estimating the probable quantity of 

 such matter. The dust collected upon the snow 

 in the polar regions has sometimes been sup- 

 posed to have originated in this way, but this 

 theory is as yet entirely unproved. Dr. Oppol- 

 zer, of Vienna, has recently investigated the 

 question whether the excess of the moon's ap- 

 parent acceleration above its computed value 

 may not arise from the mass of the earth being 

 gradually increased in this way. By a very 

 careful but somewhat abstruse mathematical 

 calculation he finds that a precipitation of 

 cosmical dust amounting to 2'8 millimetres in 

 a century, over the whole earth's surface (or 

 about a thousandth of an inch in a year), 

 would completely account for the observed ex- 

 cess of the secular acceleration. The question 

 whether a fall of this amount is possible has 

 not yet been considered by geologists. 



The Rrakatoa Eruption, and the Red Skies. The 

 autumn of 1883 was remarkable for a succes- 

 sion of brilliant sunsets of a very unusual kind, 

 in nearly every part of the world, but more es- 

 pecially in India and the Indian and Southern 

 Pacific Oceans. As the sun approached the 

 horizon, it was seen to assume a distinctly green- 

 ish aspect, and an unusual color seemed to per- 

 vade the western sky. As a rule, nothing very 

 unusual was observed during the half-hour after 

 eunset. About that time, however, an extraor- 

 dinary red glow, as from a great fire, began to 

 pervade the western sky, and in some instances 

 actually led to the belief of a conflagration. 

 The phenomenon was first noticed in India, 

 but gradually spread around the whole world. 

 The theory that found most credence among 

 astronomers was that it proceeded from vol- 

 canic dust and vapors thrown up at the great 

 eruption of Krakatoa near the end of August, 

 1883. (See METEOBOLoaY, in " Annual Cyclo- 

 paedia" for 1883, page 525.) It was found 

 that the course of the red skies around the 

 world followed closely the course that such 

 vapors might be expected to take, from being 

 wafted from place to place by the winds. Ad- 

 ditional interest was given to this view by the 

 discovery that self-registering records of baro- 

 metric pressure, in various points of Europe, 

 showed that an atmospheric wave from the same 

 eruption was carried around the earth. 



Stellar Parallax. An important addition has 

 been made at the Cape Observatory to our 

 knowledge of stellar parallax by Drs. Gill and 

 Elkin, working in concert, the latter being the 

 guest of the former at the Cape Observatory. 

 The instrument employed was the fine heliorn- 

 eter made for Lord Lindsey, for the observa- 

 tions of the transit of Venus in 1874. This in- 

 strument was purchased by Dr. Gill individually 

 and was brought into use at the Cape in 1880. 

 The following results were communicated to 

 the Royal Astronomical Society in 1884 : 



The most interesting of these results are the 

 first two. The nearest fixed star, so far as we 

 know, is a Centauri, but its distance is shown 

 to be a third greater than was formerly sup- 

 posed. The actual distance from the above 

 parallax is 275,000 times the distance of the 

 sun, a space which light would require four 

 years four months to traverse. Sirius, though 

 the brightest fixed star in the heavens, is shown 

 to be more distant than several others of the 

 fourth, fifth, or sixth magnitude, and must be 

 regarded as emitting some fifty times as much 

 light as our sun. But the case of p Centauri, 

 a star of almost the first magnitude, is yet more 

 remarkable. Its small negative parallax is im- 

 possible, and only shows that its distance is so 

 great as to elude even the refined measure- 

 ments of Dr. Gill. It can hardly be less than 

 eight or ten times the distance of Sirius, and 

 its absolute brightness must be several times 

 that of Sirius. 



Parallax of a Tauri. It does not appear that 

 any attempt has ever been made to measure 

 the parallax of a Tauri, its proper motion 

 being so small that the parallax has been sup- 

 posed very minute. In preparing his meas- 

 ures of double stars for the press, Otto Struve, 

 director of the Pulkowa Observatory, noticed 

 that they were very favorable for a determina- 

 tion of parallax, and proposed to one of his as- 

 sistants to investigate the subject. The obser- 

 vations were very accordant in showing a 

 parallax of 0-516". This result, if confirmed, 

 will place a Tauri among the three or four 

 nearest of the fixed stars. 



Motion of Stars in the Line of Sight. The spec- 

 troscopic determination of the motion of stars 

 in the line of sight, which was inaugurated by 

 Mr. William Huggins, is still continued at the 

 Greenwich Observatory. One result of recent 

 observations is quite inexplicable. The earlier 

 determinations of the motions of Sirius, both 

 by Mr. Huggins and the Greenwich observers, 

 were accordant in showing that Sirius was re- 

 ceding from our system at the rate of some 

 twenty-five miles per second. But, according 

 to the recent measures, this motion has entirely 

 ceased, many observations even showing that 

 the star is approaching us. The reality of such 

 a change in the motion must be considered in- 

 admissible. 



The Companion of Sirins. The discovery of this 

 companion is memorable as having been made 

 by Alvan Clark, Jr., in 1862, with the object- 

 glass of the great telescope which had been 

 constructed for Chicago, and as lying exactly in 



