120 



KNOWI.l.DCI. 



MAKtii. 191 ; 



pherc destroys one's capacity of juflj^'in/^ distances. 

 Many a time I have asked tourists, wlio were standing 

 on tile terrace of my ln)use, the distance of the 

 Southern Alps; tlie answer seldom exceeded ten per 

 cent, of the ei},'lity miles away. Nor do I think the 

 idea that the Cralaxy orij,'inated in the impacts of two 

 previf)usly existin},' sidereal systems would ever have 

 occurred to me in lCii,t;land. I have been here 

 nearK' one and a-half years ami have looked times 

 without numher. yet never have I seen the outline 

 of the Milky Way so clearly as to sugfjest the idea of 

 that centrifugal motion that came with such over- 

 whelming force to me as I examined the Southern 

 sky. If we could join with other rational nations 

 and bring about reduction of armaments, and then, 

 if the i)eople of England, with a true imperial spirit, 

 should act together with our overseas dominions, 

 and with the price of a Dreadnought erect an 

 observatory under those clear Antipodean skies, such 

 an establishment would enable the many unsolved 

 problems of astronomy to be ho[)efully attacked. 

 Excuse the parenthesis, but the New Zealand 

 skies are the true field for celestial observation. 



FiNDINc; ("oMKTS. 



The keen artistic eye of the astronomer readilv 

 detects a change in the stellar pattern. Perchance 

 he sees a new speck of light helping to fill a former 

 void. " What is it ? "' he asks. Is it another [)lanet 

 or an asteroid ? Is it a new star or a comet ? If it 

 is a planet or an asteroid, it will probably be found 

 auKjng the Zodiacal constellations in the plane of the 

 ecliptic. If a nova, it will [jrobably approximate to 

 the plane of the Milk\- Wa\', and occupy a permanent 

 position among the stars. If a comet, it ma\' be 

 anywhere : but because m-iny of the periodic comets 

 have been caught by the entrapping action of the 

 |)lanets, those whose orbits approach near the Sun 

 will tend to aggregate towards the plane of the 

 ecliptic. 



.•\fter a time, our astronomer, who has detected 

 the new spot of light, finds it changes its place 

 among the stars of the constellation ; hence it is not 

 a nova. If it begins to show a considerable and 

 hazy disc, with a distinct nucleus, it is probably a 

 comet. Then as it approaches the Sun a tail 

 generally appears. It has now all the characteristics 

 of a comet, and so is declared to be one by the 

 astronomical world. Then many other optic tubes 

 are directed to further study its character and to 

 plot its orbit, to photograph its form and stud\- its 

 spectrum. 



Normal C'omkts. 



Let us now examine what the countless observa- 

 tions of the astronomers and spectroscopists ha\e to 

 tell us of the salient characteristics of a normal 

 comet. Then we will use our powers of induction 

 and deduction on this assembled set of observational 

 facts, and, using also the accepted physical forces 

 and laws of nature, try and formulate an explanation 

 of the wonders of normal comets and treat further 



these explanations in the light of those that show 

 abnormal characters ; remembering always that it is 

 the normal that is our true study as regards comets or 

 any other special [ihenomena which we are attacking. 

 The abnormal we must use as being chiefly of value 

 in tending to reveal undiscovered cosmic forces and 

 unrevealed laws of nature, such as have been so 

 prodigally opened to our imagination within the last 

 decade or so. 



Let us examine the normal comet and try to 

 fathom its m\stery. 



.A NOKMAI. CoMKT. 



It consists of a nebulous star-like body or head, 

 w ith an immense luminous plume or tail : the tail is 

 frequently curved, it is not infrequently multiple, 

 and where its several parts are unequal in volume 

 the thinner portions tend to be the straightest. 



.\s the comet travels in its orbit, the tail is almost 

 alwa\s directed away from the Sun. The tail is 

 generally curved in such a way as to suggest a lag, 

 as though the tail had been produced b\" an impulse. 

 and the luminous effect had taken time to travel. 

 The appearance of some comets is not altogether 

 unlike a rocket, but the rocket leaves its tail behind 

 it. whilst the comet travels with its tail side on. 

 The nearer to the Sun the greater the tail grows to 

 be. Figure 125 shows the normal character of a 

 comet as it passes the sun in the perihelion i)ortion 

 of its orbit. 



The drawings of man}- comets show a kind of 

 series of parth' ensphering shells being projected 

 from their heads towards the sun. 



TlCNlITV OK COMICTS. 



The liead even of a comet is of extreme tenuity, 

 so that stars have been seen completely through 

 some of them in their densest parts. Comets ha\e 

 also passed in front of the Sun, yet no sign of any 

 eclipse effect has been seen : nor e\en the slightest 

 darkening has been observed. These two facts, 

 combined with others, suggest that comets are of the 

 character of a swarm of meteors. 



A comet has been known to part into two, and 

 travel as distinct parts, and finally dissipate 

 altogether. The Earth in its orbit intersects the 

 orbits of some comets, and on the days of nearest 

 approach the sky is lit up w ith a brilliant display of 

 meteors, with an effect as though they shot in every 

 direction from a radiant point. (See F'igures lib and 

 127>. Some of these displays have been of extreme 

 brilliancv and beauty. .Astronomers and tra\ellers 

 who have seen such phenomena at their best, 

 describe them as of such superb grandeur as to out- 

 shine the most magnificent pyrotechnic display. 

 Those of us who have seen only ordinary examples 

 of these exhiliitions. know how glorious e\en such 

 sights are. 



Comets api)ear to shine by reflected light, but as 

 their luminosity- often increases more quickly as 

 the\- approach the Sun. then the law of the in\erse 



