Jan. 16, 1SS5.] 



♦ KNOWLEDGE ♦ 



41 



iv...uAZINE OF SCIENCE 



PUINLYWORDED-EXACTLYDESCRIBH) 



LONDOX: FBIDAY, JAX. IG, 1885. 



Contents uf -No. 1u>. 



PAGE 



Xwded St»r SurreTe. By E. A. 



Piwtor .' 41 



Th» Workshop at Home. (lUiis.).. 43 

 Geometrical Measurement. By 



B. A. Proctor 44 



The ChemistTT of Cookery. 11. 



By W. Matti'eu WiUiama 43 



Other Worlds ihan Ours 47 



Electro-pUtinj. Bt W. Slingo 48 



Weather Forecasts of 1S84 49 



PAGB 



Zodiacal Maps. By I!. A. Proctor.. 61 



The Sun's Heat. By R. A. Proctor Bl 



Modern Domestic Economy 53 



" Carrvinc " Tricycles 54 



Editorial Gossip 65 



Reviews 55 



Face of the Sky. By F.R.A.S 66 



Correspondence 57 



Our Inventors' Column 59 



Oar Chtss Colimm 60 



NEEDED STAR-SURVEYS. 



By Richard A. Proctor. 

 (Continued from p. 8.) 



SIR JOHX HERSCHEL naturally rejected the idea 

 that the features of the Magellanic Clouds are to be 

 thus explained. Even if we could suppose, he said, that 

 one of these clouds had the shape of a long cylinder whose 

 axis was directed exactly towards our solar system, it 

 would be impossible to suppose that the other is to be 

 similarly interpreted, that a similar strange chance had set 

 a second long cylinder of stars in space with its axis bear- 

 ing exactly on the sun's family. lie does not seem to 

 notice the yet more fatal objection that each Magellanic 

 Cloud would have to be something more than a cylinder of 

 stars so situate : at an immense distance beyond each 

 cylinder, and exactly in the prolongation cf its axis, there 

 would have to be a cloud of star-clouds, to account for the 

 multitudinous nebul.'e within the nubecula. But Sir John 

 Herschel pointed out objections enough to convince every 

 one that the Magellanic Clouds have in reality the rounded 

 form which they appear to have. Then he went on to 

 bhow that this being so, the distance of the remotest object 

 in either nubecula does not exceed the distance of the 

 nearest, by more than as ten exceeds nine : within these 

 narrow limits of distance, he say.s, lie all orders of stars 

 from the seventh down to the faintest visible in the great 

 gauging telescope, nay even to milky light completely 

 irresolvable into stars, besides all orders of nebula:, cluster- 

 ing, irregular, round, elliptical, resolvable and irresolvable, 

 bright and faint. 



All this shows that science had been quite mistaken in 

 supposing that the stellar universe consists merely of stars, 

 not dififering greatly in size, or much more richly strewn in 

 some parts than in other.s. Just as the old idea of the 

 solar system formed by Copernicus, as a central body 

 circled round by six planets, has long since had to give 

 way to the diversified system recognised by the astronomy 

 of to-day, with its sun and giant planet>-, terrestrial jilanets 

 and asteroidn, large moons themselves as worlds and small 

 moons like those of Mars, the ling system of Saturn, and 

 finally (at present at least) the Conietic and Meteoric 

 systems, so has the old and simple idea of the stellar 

 galaxy had to give place to the conception of a mo«t 

 complex system, with giant suns, suns like our own, and 



minor suns, double, triple and multiple suns, clustering 

 aggregations, streams, branches, clouds, and complex 

 groupings of stars of all orders, with nebuho of all kinds, 

 stellar and gaseous, round, oval, ring-shaped, spiral, and 

 irregular. 



And hero I would pause for a moment to correct an idea 

 which has been very frequently suggested in terras implying 

 that it is the obvious ex|ilanation of what we see instead 

 of being absolutely inadmissible. ]n almost all works ot 

 astronomy, when the varying degree of resolvabiiity within 

 cloudlike regions of star space has been mentioned, we find 

 the minute points of light recognised when resolution is 

 effected, treated as if of necessity they were suns like our 

 own, each girt round by its family of worlds But this is 

 altogether incorrect. It is absolutely certain that stars 

 strewn through space like our sun and his fellow-suns (the 

 individual stars of our constellations), could never appear 

 as a milky, unresolved nebulosity : for the .simple reason 

 that with increase of distance the individual stars, 

 even were they as large as Sirius, would disappear 

 long before they drew clo.se enough together to present the 

 appearance of irresolvable cloud. This is easily shown. 

 Suppo.se the stars visible to the naked eye to be all suns 

 like our own, the faintest being therefore about a hundred 

 times farther away than the brightest. Then for that 

 spherical region of space to bo removed to so great a 

 distance that the whole set of some G,000 stars formed a 

 cloud as large as the moon, the centre (our sun suppose) 

 would have to be removed to a di.stunce exceeding 

 more than a hundredfold the entire diameter of the 

 sphere, and therefore exceeding more than two hundred- 

 fold the distance of the faintest visible star from our 

 solar system. All those G,000 stars then would lie not 

 only enormously beyond our unaided vision, but beyond 

 the range of telescopes of considerable light-gathering 

 power. For, removing the faintest, to a distance two 

 hundred times greater would correspond to reducing its 

 light to one-eight millionth part of its present amount. 

 But six thousand stars strewn over such a portion of the 

 heavens as the moon covers, would be easily separated : the 

 average distance between them would be twenty seconds of 

 arc, and double stars separated by such a distance as that 

 are considered quite "coarse." Tiius, long before the 

 individual stars were merged into each other by the effect 

 of distance, each would be separately undiscernible. Now 

 it should hardly be necessary to point out that to speak of 

 stars separately invisible, but lying at distances easily dis- 

 cernible (as such), forming a milky light, however faiut, is 

 utterly absurd. It is essential for the production of such 

 milky light as we see in the galaxy, that the apparent dis- 

 tances of the separate stars should be lost through effect of 

 distance before the st.ars cease to be visible. 



As the jioint considered in the las,t paragraph is of great 

 importance, and very little understood (or noticed, if under- 

 stood), I give the following illustrative tests : — 



9 • * 



« o « 



e « • • 



Here vre have three groups of dots all of tbe same sizo, 



