May 27, 1892.] 



SCIENCE. 



299 



indeed, to be seen whether the whole of its supposed trans- 

 latory speed may not really be of a circulatory character. 



Dr. Chandler's theory does not rest wholly on the cyclical 

 inequalities of Algol's light-changes. He alleges also in its 

 support periodical disturbances of proper motion, brought to 

 view by a careful discussion of all the observations of the 

 star, from 1753 to the present time, and indicating, in his 

 opinion, a combination of elliptical travelling with a pro- 

 gressive advance. But the average proper motion of Algol 

 is so very small— less than 2" of arc a century — that varia- 

 tions or irregularities in it can at present be regarded only 

 as an interesting possibility. They would give, if confirmed, 

 2.7" for the longest diameter of the ellipse into which the 

 wide orbit traced out by Algol round its unseen primary is 

 projected upon the sky. And since this little span repre- 

 sents an actual expanse of 38 earth-to-sun distances, or "as- 

 tronomical units," it implies a parallax for the star of 0.07", 

 corresponding to a distance of nearly 47 light-years— a 

 statement that is in many ways worth thinking about. 

 Although claiming only qualified credence, it nevertheless 

 conveys the upshot of assuredly the most promising attempt 

 yet made to determine, by indirect means, the parallax of a 

 star. In itself, too, it seems probable enough. Assuming 

 its accuracy, we gain the information that Algol emits 63 

 times as much light as the sun, which, in its place, would 

 show with little more than the brightness of a seventh-mag- 

 nitude star. The famous variable, moreover, according to 

 Dr. Vogel, is just one million miles in diameter, so that it 

 presents only once and a third the solar radiating surface; 

 yet it is, as a light-giver, 63 times more effective. The re- 

 markable conclusion follows, that Algol is intrinsically 47 

 times more brilliant than the sun. The emissions from its 

 photosphere are, per unit of area, 47 times more powerful. 

 And should its parallax eventually — as seems not unlikely 

 — prove to be smaller than 0.7", this disparity will be still 

 further enhanced. 



By means, accordingly, of investigations of this nature, 

 more fully and securely carried out, the question as to com- 

 parative stellar brilliancy may finally obtain a sufficiently 

 satisfactory answer. It is a very important one. The pro- 

 cess by which photospheric light is manufactured is still 

 largely enigmatical, but the ideas commonly entertained 

 about it are not easily compatible with the existence of con- 

 siderable differences in the shining faculty of photospheric 

 shells presumably identical in point of chemical composition. 

 Reliable evidence of such differences has not hitherto been 

 available. That light-power in stars bore no fixed propor- 

 tion to mass was patent in numberless examples; but the 

 density, consequently the dimensions of the emitting bodies 

 remaining unknown, it could not be determined whether 

 distension of substance, or innate strength of incandescence, 

 was more concerned in producing a great sum-total of light 

 relative to quantity of matter. The indications, however, 

 now derived from Algol are overwhelmingly in favor of the 

 latter alternative. 



The primary member of its system, even if illuminated 

 solely by the borrowed rays of its brilliant neighbor, may 

 not, Dr. Chandler thinks, be out of reach of telescopic dis- 

 covery. But his hopes, in this case, appear somewhat chi- 

 merical. It is not difficult to show that, under the circum- 

 stances supposed, a body of planitary constitution could not 

 possibly be disclosed by any optical means at present avail- 

 able. Its position-angle relative to Algol is just now, we 

 are told, 32^, while its distance from the same star is in the 

 inverse ratio of its mass. This is considered by our author 



to be indeterminate; but it is not so, unless we reject Dr. 

 Vogel's value for the combined mass of the close pair form- 

 ing the variable. Assuming its approximate correctness, 

 and that Algol and its immediate attendant accordingly 

 contain two-thirds the solar quantity of matter, and admit- 

 ting, further, that they revolve together, at a distance of 

 nineteen astronomical units, in a period of 131 years, round 

 their common centre of gravity with another body, it follows 

 that the m;iss of that body is about equal to that of the sun, 

 and that it circulates at twelve units of distance from the 

 gravitational centre of the system. It should be found, this 

 being so. if found at all, at an apparent interval of rather 

 less than 2" from Algol. The real gap of spsce separating 

 them — the radius, that is to say, of Algol's relative orbit — 

 would be measured by thirty-one radii of the earth's orbit; 

 and the effectiveness for visual purposes of a still problem- 

 atical body, shining by reflected light alone, can hence be 

 estimated. If of the same density with Algol, it presents a 

 disc of fivefold area, which, endowed with Jupiter's high 

 reflective power, or an albedo of 0.62, would possess a total 

 lustre ^.ji^.innr '■b^' ^^ ^^^ original source of its radiance. 

 This is equivalent to saying that it should be fainter by six- 

 teen stellar magnitudes. Yet the suppositions introduced 

 above are perhaps unduly favorable to conspicuousness. 

 Evidently, however, an eighteenth-magnitude star, in the 

 close vicinity of one of the second, is far below discernment 

 with any telescopic or photographic powers likely to be in 

 use for a considerable time, if ever; so that visual confirma- 

 tion of Dr. Chandler's theory can only be looked for if the 

 unknown mass it has brought ideally into existence be in 

 some degree self-luminous. 



That theory, as he remarks, " has a much wider cosmolo- 

 gical meaning than the mere explanation of the phenomena " 

 of a single star. Most " eclipse- variables " exhibit irregu- 

 larities of the same type with those of Algol, and which 

 will doubtless prove amenable to a similar explanation. 

 Moreover, an incalculable number of stars which, from our 

 point of view, escape eclipse, unquestionably belong to sys- 

 tems organized on the same general plan. One such, in- 

 deed, is already known in aVirginis, a first-fruit of discovery 

 in this particular branch; and Procyon, perhaps, is one of 

 many others essentially resembling it, although inaccessible 

 to spectrographic research, because revolving in planes 

 nearly perpendicular to the line of sight. Thus the intimate 

 association of dark and bright bodies of the same order of 

 mass would appear to be no exception in the universal order. 

 And this scarcely allows us any longer to regard a sun-like 

 condition as representing simply and solely a stage in the 

 condensation of a primitively nebulous mass. Some further 

 conditions are plainly needed to produce the brilliant and 

 concentrated evolution of light characteristic of " suns." 



Dr. Chandler concludes his valuable paper with an appeal 

 for micrometrical measures of Algol stars, adapted to detect 

 and determine possible systematic disturbances of their 

 proper motions. Measures of the kind might, in his opinion', 

 lead to highly significant results, which would probably, in 

 the case of T. Cygni, be reached with particular promptitude. 

 " If the research gave favorable results in this instance," 

 our author continues, "it could then be extended to A Tauri, 

 which appears to be also a promising candidate." It is to 

 be hoped that the suggestion will not remain unheeded. 

 Owners of heliometers could hardly turn them to better ac- 

 count than by applying this simple criterion to an hypothesis 

 which opens yet one more road through the daily widening 

 field of sidereal discovery. Miss A. M. Ci^EEKE. 



