Feb. 13, 1885.] 



♦ KNOWLEDGE ♦ 



119 



AN illustrated" 



MAGAZINE OF SCIENCE 



PULNLYWOFxDED -EXACTLYDESCRIBED 



ZOXBOS.- FRIDAY, FEB. 13, 1885. 



COSTKNTS OF NO. 172. 



X«d*d Stir-Sorreyt. Bj K. A. 



Proctor lis 



The Entomolo^ of a Pond. ilUus.) 



Bj K. A. Butler 120 



Tricycles in ISSS. (Ulut.) By 



John Browning Vll 



The Be^ning ot Life. By B. A. 



Proctor 123 



The Workshop at Home. (Hint.) 



By a Wortinj: Man 121 



Cha'ts on Geometrical Measorement. 



By R. A. Proctor 125 



Electricity Man's Slave. By T. A. 



Edison' 127 



The Ealcrala. I. By Edward 



Clodd 129 



First Sl)ir Lessons. (Withilup.) 



By R. A. Pmctor 130 



Chapters on Modern Domestic 



Economv 132 



Editorial Gossip l:a 



Reviews 131 



Face of the Skr. ByF.K.A.S 136 



Ephemcris of Encke's Comet 13ti 



Miscellanea \'M\ 



Correspondence 137 



Oar Inventors' Column 139 



Oar Chess Column 140 



NEEDED STAR-SURVEYS. 

 By Eichard A. Proctok. 



{Continued from jj. 83.) 



THE proper way of applying the test by those statistical 

 methods which Struve loved, — but ■which I reject as 

 utterly inadequate for any but the simpler problems of 

 stellar distribution, — would clearly have been to have 

 counted the stars in the Milky Way (or on a galactic zone 

 of such and such breadth) noting the area of the region 

 thus dealt with, then to have counted the stars in the 

 regions of the heavenly sphere outside the Milky Way (or 

 that galactic zone) noting the area thus dealt with, and 

 then to have compared the wealth of stars in these two 

 areas — the galactic and the non-galactic. Supposing the 

 charts or catalogues used for this work to have n suited 

 from a fairly uniform survey of the heaven?, or were it 

 even only of the northern hemisphere, with a telescope of 

 small power, the result Struve would have thus obtained 

 would have been satisfactory enough. 



This was not what he did. Probably he had not time. 

 The process he actually applied indicated certainly that he 

 was somewhat pressed for time, since it could not have 

 taken him much more than ten minutes. He took a certain 

 catalogue of stars down to the ninth magnitude. In these 

 the stars to a certain distance on either side of the equator 

 were arranged in the order of the twenty-four hours round 

 the ^celestial sphere (technically in order of their Plight 

 ascension) and numbered from first to last. The number 

 of stars in the first hour was thus indicated in the catalogue 

 as the number of the last star within that hour, the number 

 in the second hour was obtained by subtracting the number 

 of the last star in the first hour from the number of the 

 last star in the second hour ; and so on for the numbers of 

 stars in the third, fourth, fifth hours, and so on, up to the 

 twenty-fourth. Twenty-three sublractions gave Struve all 

 the statistics he employed. He found that the fifth, sixth, 

 and seventh hours on one side of his zone, and the eleventh, 

 twelfth, and thirteenth on the 'other, were richer in stars 

 than the rest, in such degree as to show that the Milky 

 Way, which crosses the equatorial zone aslant at those 

 hours is richer than the non-galactic parts of the heavens. 



But it is hardly nece.-^sary to say that the real rtilative star- 

 wealths of the ]\lilky Way and of parts outside it could 

 not be properly indicated by so rough an inquiry as thi.-;. 

 It atlbrded an independent proof of the general law which 

 Sii- W. Ilerschel had already recognised at the bt^ginning of 

 the present century ; but it scarcely added more to our 

 kuowlcdge. 



My own inquiry into this ])articular point involved 

 rather more labour. I proposed at first to use the cata- 

 logues aud charts of Argelander, in which 324,198 stars 

 (down to magnitude 9-10) are included, taking the nume- 

 rical distribution over the Milky Way, and then over 

 regions outside of it. But a few tests showed me that 

 while this method would involve almost as much work as a 

 process of actual charting, it would be much less satis- 

 factory. I determined, therefore, after consulting the 

 venerable Sir John Herschel on the subject (this was 

 but a year before his death), to chart every single star of 

 the 324,198 in its proper place, on an equal surface projec- 

 tion of the northern hemisphere, — that is, a projection in 

 which equal surfaces on the heavens were represented by 

 equal areas in the map. I laid down in pencil a series of 

 radial lines a degree apart (3t!0 in all), and ninety-two 

 concentric circles at one - degree distances (gradually 

 diminishing outwards), corresponding to the particular 

 projection which I was employing. Then in the 33,000 

 spaces thus formed I marked in the stars shown in the 

 corresponding 33,000 spaces of Argelander's forty charts. 

 Thus I had, charted on a uniform scale, all the stars 

 observed by Argelander and his assistants, during seven 

 years, in their survey of the heavens from the north pole 

 to a distance of ninety-two degrees all round, or to two 

 degrees south of the equator. 



The work occupied me in all almost exactly four hundred 

 hours. 



But the result was, I think, well worth the trouble. 



In the first place, I note a peculiarity in the large chart 

 of 324,198 stars, which attracts attention at once, yet is 

 manifestly accidental, or due, rather, to the method in 

 which the original series of 4<l charts, and the single chart 

 itself, were formed. The peculiarity is a defect, though of 

 little importance, — yet interesting as illustrtting the points 

 which have to be attended to in such woik. The circular 

 chart seems to show in places multitudes of concentric 

 streaks produced by the aggregation of stars along certain 

 very narrow zones, concentric with the boundary of the 

 map, — that is to say, having the north polo of the heavens 

 as their centre. As my fiiend Professor Young pointed 

 out, there cannot conceivably be any real tendency in the 

 stars to form circular zones around the pole as centre, or 

 along declination parallels : yet such a tendency seems 

 manifestly suggfsted by the appearance ot the great chart 

 when closely studied. So far as the broad results sought 

 and obtained are concerned, this peculiarity is of no more 

 weight than the direction of the linear .streaks by which in 

 an engraving effects of light and shade are produced. Still 

 until or unless the peculiarity is explained, it detracts 

 something from the confidence with which those broader 

 results are accepted. 



Not really existing in the heavens, how does this pecu 

 liarity of star-distribution come to appear in the chart ? 

 The answer, though not at a first view obvious, is simple 

 enough. The wonder would be if the peculiarity had not 

 shown itself. Argelander and his assistants, in their survey 

 of the northern heavens, swept the skies in circles round 

 the north pole, after the manner of survey with the 

 equatorial telescope, which works in that sort (its main 

 axis being directed polewards). Now herein is at once a 

 possible cau-e of circular striation in the resulting charts, 



