128 



SCIENCE. 



[N. S. Vol. XVIl. No. 421. 



adequacy of the speed of light to explain 

 the phenomena. If the distance of this 

 star is only 400 times that of « Centauri, 

 the speed of the apparent expansion must 

 have been ten times that of light. 



Of all agencies known to be propagated 

 through space in time, light is the swiftest 

 in its motion. We may, therefore, say 

 that no known cause coming into action 

 in February, 1901, could, within the 

 twenty-two months which have since 

 elapsed, have emanated from the star so 

 as to make itself felt outside of a sphere 

 which, at the distance in question, would 

 subtend to our eyes an angle of more than 

 four minutes in diameter. We seem, 

 therefore, forced to the conclusion that 

 either the illumination or nebiilosity sur- 

 rounding Nova Persei during the summer 

 of 1902 existed independently of the oiit- 

 burst of the star, or there exists in the 

 universe a cause susceptible of transmission 

 with a speed several times that of light. 



When we look closely into the matter, 

 we find some difficulty in proposing any 

 hypothesis based on the known action of 

 natural agents. A continual course of 

 self discipline is necessary to enable us to 

 appreciate the real significance of the ques- 

 tion. The facts, as I understand them, are 

 briefly these: We see by photography an 

 object in the heavens in which certain 

 changes are going on consisting of varia- 

 tions in the appearance of the illuminated 

 portions. Daj' after day we see that a 

 certain illumination beginning at a point 

 A, no matter where, spreads to a point B. 

 and perhaps a point of light, C, begins to 

 show itself. The natural conclusion is 

 that something is being propagated. The 

 point B has received an emanation from 

 A and the point C has not appeared spon- 

 taneously, but has been connected with 

 something going on at some other point, 

 perhaps the central star. In attributing 

 this propagation to that of anything but 



light and radiant heat, we are met by the 

 difficulty that all other known natural 

 causes which could have operated in such 

 a case fall short of this in their speed of 

 transmission. 



Whichever way we turn we meet with 

 difficulties which seem insuperable in con- 

 structing any theory that will explain the 

 observed phenomena. The light theory 

 which I have mentioned is rendered more 

 unlikely from the fact that the latest re- 

 searches upon the Lick photographs seem 

 to show that the emanation did not go out 

 in straight lines with nuiform velocity, but 

 branched oft' here and there, sometimes in 

 one direction and sometimes in another, 

 with varying speed. There is a difficulty 

 in attributing the apparent expansion to 

 the motion of light which seems yet greater 

 than this. The speed of light is perfectly 

 uniform. The outburst was extremely 

 sudden, it being only two or three days 

 from the time when the star became visible 

 until it reached first magnitude. Under 

 the circumstances the outgoing light-wave 

 would have been a well-defined spherical 

 surface, brighest at a point so near the 

 actual surface that its extent would not 

 be visible at such a distance. The star 

 faded away at a rate which reduced it to 

 one half in a very few days and again to 

 one half in a few days more. The light 

 emanating from such an object would, 

 therefore, have presented to our eyes the 

 appearance of a well-defined luminous cir- 

 cular disc, brightest at the circumference 

 outside of which all would have remained 

 in complete darkness. It is true that, 

 owing to the difference of density of the 

 material reflecting the light, the disc would 

 not have been uniform. It might have 

 many gaps here and there and present a 

 cloudy appearance. But with all these 

 differences the boundary would have been 

 as well defined as if the disc had been 

 turned in a lathe. 



