BiCKERTON. — Evidence iii favour of Impact. 4G7 



three bodies, that he suggested a local disturbance as a solu- 

 tion. Obviously this identity of spectra must follow with a 

 grazing impact. Each of the two bodies must entangle a 

 great deal of heated matter from the other, and the middle 

 body is, of course, actually made up of parts of the two origi- 

 nals. 



Every element represented in the spectrum had its line or 

 lines in triplicate — one being very broad and having two 

 others superimposed on it. It is evident that a body expand- 

 ing with incredible velocity in all directions, as T have de- 

 monstrated the central body must do, is bound to give broad 

 bands, because of the molecular motion in all directions. 



The new star became a planetary nebula. Gregory states 

 in a long article in " Nature " that this is demonstrated in two 

 totally different ways ; and Professor Bernard, the discoverer 

 of Jupiter's 5th satellite, says that it had become a planetary 

 nebula of 3secs. of arc, with a tenth-magnitude star in 

 the centre. This observation shows that at this stage the 

 chief light was not from the nebula but from the star. Of 

 course, this is exactly in accordance with the theory of im- 

 pact, suggesting, as the latter does, a gradual and steady 

 diminution in the intensity of the third body and the occa- 

 sional reappearance of the struck stars. Professor Bernard 

 also states that the nebula was not there at first. Hence the 

 prediction that a partial impact must produce a hollow shell 

 of gas or planetary nebula is in exact accord with the observa- 

 tion of Nova Auriga. The new star must have been produced 

 by the impact of two very large orbs. Probably the amount 

 sheared off may have been many times as large as our sun ; yet 

 it was not likely to have been at all a large fraction of the 

 whole — possibly not large enough to cause the two suns to 

 become orbitally connected into a double star ; nor is it even 

 likely to have been large enough to allow the resultant planetary 

 nebula to become permanent ; but the data at our disposal 

 are rather conflicting. Taking the average of the best observa- 

 tions, I have calculated that the two impacting bodies were 

 respectively four thousand and eight thousand times the mass 

 of the sun ; that the velocity of the smaller body at impact 

 would have been about 4,000 miles per second, and of the 

 larger one about 3,000 miles per second. This would give for 

 the swiftest a velocity of 600 miles per second sixteen days 

 after contact. There seems every reason to suppose that a 

 very large proportion of the luminosity of the two resultant 

 variables will die down within the first year or two. At the 

 same time, there is a large probability that they will be 

 periodically bright enough to show themselves for scores of 

 years. In about ten years their habits will have become 

 regular enough to enable us to predict their ultimate durability. 



