262 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Nov., 1904. 



distance through which this force extends, gives us an 

 energy so great that, without any original motion, a 

 particle falling from the nearest star upon the sun 

 would reach it with a velocity of three hundred and 

 ninety miles a second. This \elocity would possess 

 an energy hundreds of millions of times greater than 

 that of an express train, and the temperature produced 

 li\ the stoppage of the motion would excel that of an 

 L'lectric furnace a score of thousands of times. 



Hence, in the collision of suns we ha\e an agent 

 that may generate energy sufficient to cause the sun to 

 explode, but so enormous is the mass of a sun, that 

 the energy of collision has been shown to be too small 

 to blow the sun into a nebula ; but the probabilities of 

 a direct, complete collision between suns is small in- 

 deed. Any original motion or any attraction of other 

 bodies acting during their fall towards one another, 

 would tend to makcthe impact of a tangential charac- 

 ter, and it is upon tlie study of tangential impact that 

 the solution of our problem depends. The velocity 

 with which two suns would sweep past one another 

 would be so great tiiat a slight graze would not stop 

 them. They "would tly past one another, scarred by 

 the encounter ; but the portions that lay in one 

 another's path, and that did actually come into collision 

 would be swept from the reniaintler, would coalesce, 

 and would form a new Ijody in space. The 

 tremendous motion would Ijc con\erted into heat, and 

 the mass of the new hod\ , if the graze were not deep, 

 might be so small that the explosi\e pressure produced 

 would blow it into a nebula that would continue to 

 expand with an enormous \elocity, and every particle 

 be finally dissipated into free space ; in some cases 

 leaving the very universe itself. 



It is thus seen that the numbers and distribution of 

 the stars must, on the demonstrated laws of Nature, 

 produce an explosion ; and it is highly probable that 

 all the so-called temporary stars that have appeared at 

 intervals in the heavens, usually increasing in brilliancy 

 for some hours, or a day or two, and then gradually 

 disappearing, are caused by p.artial impacts of stars 

 or, in most cases, of dead suns. For all these bodies 

 have similar spectra crossed with doubled lines, the 

 one showing recession, and the other approach, 

 indicating the two scarred suns that have struck one 

 another; whilst the brilliant continuous spectrum 

 seen in all new stars, for some time after the outbreak, 

 is due to the mass of flaming gas that must expand at 

 the rate of some milHon of miles an hour. 



The \'elocity with which these bodies pass one 

 another would cause the impact to be o\er in an hour 

 or less ; and in this time a body is produced with a 

 higher temperature th.an that of any ordinary star. 

 'I'his IjrilHant body would soon expand until the globe 

 of (ire would be thousaiuls of limes the \olume of the 

 sun. 



Hence we need not be surprised ihat Tycho Rrahe's 

 new star grew to be more brilli;mt than Jupiter, even 

 more briili;mt llian \'enus at qu.'idrature ; so intense, 

 in fact, as to be \isiljle at noonday. Nor need we 

 wonder at its disappearance, for the flight of its myriad 

 molecules all travelling from the point where the ex- 

 plosion occurred, would rapidly tend in their radial 

 outrush to become ])arallel, and the molecules con- 

 sequently cease to strike one another save at intervals ; 

 and as molecules only radiate immediately after en- 

 counters, it is obvious that, as these encounters become 

 fevyer in number, the luminosity of the mass would 

 lessen and go on lessening until it was absolutely lost 

 to vision. 



Herschel has told us that the only possible explana- 

 tion of the character of the many planetary nebula that 

 he discovered was that they were hollow shells of gas. 

 Every stellar explosion that is produced by a partial 

 impact must result, at one stage of its history, in a 

 planetary nebula that may be permanent or evanescent 

 according to the attractive power of the new body as 

 compared with its temperature. 



Thus evanescent planetary nebula would be produced 

 by slight grazes, whereas a deeper graze might pro- 

 duce a permanent planetary nebula, and still deeper 

 grazes result in a large ratio of the molecules being 

 attracted back, and producing a star in the centre of 

 the nebula. Examples of this arc comparatively 

 numerous in the celestial vault. 



.So that our observers were doubtless right in the 

 conclusion they came to that " Nova Persei " was a 

 celestial explosion in which a star had been blown to 

 pieces. And this fragment of the study of impact 

 shows how important an agent impact is in astronomi- 

 cal evolution, for it must be remembered that all kinds 

 of impacts may take place, from a mere graze up to 

 a complete impact. Impacts may take place between 

 dead suns or lucid stars. They may take place between 

 meteoric swarms, or between star clusters. The impact 

 of nebuke may range from a mere graze through deep 

 cuts, up to entire coalescence ; and every form of im- 

 pact save direct centre to centre must result in rota- 

 tion, and obviously furnishes an explanation of the 

 spiral character of so many thousands of nebulae. 

 .Again, such vast bodies as the two magellanic clouds 

 may be approaching one another, and after countless 

 ages may imp.'ict, and should they strike deep enough 

 into one another, coalescence of a whirling character 

 would result, giving a galaxy of stars of a double 

 spiral character, and spreading the poles of the ring 

 with masses of nebulous matter, a configuration that 

 exactly corresponds with the structure of our universe, 

 and hence may we not ask the question, " Is not our 

 visible uni\erse a result of the coalescent impact of 

 two previously existing universes, and if so may not 

 such cosmic systems exist in endless number through- 

 out the infinity of space? " 



.Such are the lofty conceptions that develop them- 

 selves from the study of impact, carried fearlessly to 

 its legitimate conclusions. 



PKotogroLphy. 



Pure and Applied. 



By Chapman Jones, F.l.C, E.C.S., ivc. 



The Use of Colour Screens n'llh a Loiu Sun. — In the 

 September number I wrote: — "As the sun gets low 

 the daylight gets markedly more yellow, and we have 

 from time to time been instructed that the excessive 

 blue sensitiveness of gelatino-bromide plates becomes 

 so far negatived on account of this change, that it is 

 not necessary to obviate it by the use of a yellow or 

 orange-coloured screen. Whether or not this is so 

 depends on what the photographer wants. If he seeks 

 to photograph an evening effect as if it were lit by 

 such light as given by the sun only when he is high 

 up in the heavens, while the general effect is such as 

 can be obtained only when he approaches the horizon, 

 then he may omit the coloured screen. But if his aim 

 is to photograph the scene before him as it is, there is 



