March. 1912. 



kno\vlI':dgk. 



i|uares suggests they probably become self-luminous might be expected : because even supposing fully si.xty 



per cent, of comets were hyperbolic, we might reason- 

 ablv expect to appear to see ten or even fifty times 

 as many that were not hyperbolic ; as once a comet 

 is entrapped it will appear again and again, whilst 

 an hyiierbolic comet comes once and goes for ever. 

 Our solar system has probabK' had some scores of 

 millions of years in w hich to 

 entrap comets. Hence it is 

 of supreme im[)ortance to 

 very carefully look for hyper- 

 bolic comets. The discover}' 

 of even one in a lifetime 

 would be important evidence, 

 and tell us much of the 

 origin of these bodies. 



.IS thev become subject to the Sun's tidal action and 

 the heat of im[)act, and as the light of electricity 

 proiiiirt-il b\' friction is developed. 



Tni: Mass of Co.mkts. 



Comets have approached very close to planets ami 

 their moons, without any 

 .listurbing effect having been 

 able to be demonstrated : 

 hence in a cosmic sense they 

 cannot be of great mass. 

 All the evidence suggests 

 that they are small meteoric 

 swarms, so small that they 

 have been called " pinches 

 of cosmic dust." But our 

 earth has also been called " a 

 speck of cosmic dust." yet 

 we know its mass is far from 

 insignificant. 



So with the comets. It 

 appears to me that their real 

 mass must be considerable ; 

 for unless there were great 

 mutual attraction, the Sun's 

 differential pull on their 

 several constituents must dis- 

 perse them. Had the\" fully 

 one-millionth the mass of the 

 Marth it is probable that under 

 tile conditions observed their 

 perturbing action could not be 

 measured. Vet such a meteoric swarin would have 

 I mass of six thousand millions of millions of tons, 

 iiid this I imagine is what we must accept to be the 

 order of the mass of a normal 

 comet. .Although the passage 

 of the earth through a comet's 

 tail has not been able to be 

 detected when such an event 

 has occurred, if the earth 

 were struck by the actual 

 nucleus of a comet. I imagine 

 tile inhabitants would ha\e a 

 very warm time, with possibly 

 no one left to tell the tale of 

 its temperature. 



Figure 126. 

 The above diagram illustrates a set of parallel 

 meteors, a part of a train, plunging into our 

 atmosphere. The apparent radial direction is 

 an effect of spherical perspective, as is also the 

 lengthening of their curves, as they increase in 

 distance from the radial point. 



Thk Sl'KCTRA OF COMETS. 



A good deal of conflict 

 seems to exist as to the 

 spectra of comets. There has 

 alwa\s been a tendenc\- to 

 ascribe much of their ob- 

 served effect to carbon and 

 its compounds. Professor 

 I'owler has quite demon- 

 strated the existence of 

 carbonic oxide in both the 

 heads and tails of some 

 comets : but we require to 

 know a good deal more 

 than we do about comets' 

 spectra. 

 The SuKPRisiNc; \'akiety of the Phenomena 

 Presented by Comets. 

 The above are some of the more salient and 

 characteristic properties of 

 comets, but they are very ex- 

 traordinary objects, and they 

 teem with surprises and have 

 extraordinary varieties of 

 structure (See Figures 129 and 

 1 Jl) : so varied, indeed, that it 

 looks as though a long time 

 must elapse before all of even 

 their generic characteristics 

 shall be understood and receive 

 a satisfactor\- solution. 



DiSTlRl'.ANCI-; AND DISTOR- 

 TION OF Comets' Tails. 

 The tails of comets not 

 infrequently seem to be 



subject to a tearing or distorting action. They 

 sometimes temporarih' s])lit into parts, or become 

 irregular and roughly nucleated. They appear to 

 he encountering some disturbing force in their 

 passage through space. (See Figure 128). 



The Orbits of Comets. 

 The orbit of the majorit\' of comets is either 

 elli|)tic, or closely approximates to a parabola. This 



.A Meteor heated by friction of the atmos- 

 phere and its volatiHzed train. It has not 

 yet split or exploded. Meteors frequently do 

 so, and the parts scatter. 



Dense Cosmic Masses. 

 It is prettv clearly evident 

 that comets are meteoric 

 swarms, and it is almost 

 certainly the fact of their fragmentary character that 

 causes their brilliancy. It seems clear. howe\er, that 

 single bodies of many times their mass might easily 

 pass through our svstem without their being seen. 

 \\'hen such a dense mass struck the Sim it w ould act 

 as a detonator, that would cause the solar energy 

 to develop a most surprising solar disturbance. 



EXPLANATION'S. 



W^ 



now trv to offer some tentative suggestions 



