THE NEW STAR WHICH FADED INTO STAR-MIST. 133 



the planetary and other gaseous nebulae. Any hypothesis 

 accounting for its existence in the spectrum of the faint blue 

 starlike object into which the star in Cygnus has faded ought 

 to be competent to explain its existence in the spectrum of 

 those nebulae. But this hypothesis certainly does not so 

 explain its existence in the nebular spectrum. The nebulas 

 cannot be suns which have died out save for the light of 

 gaseous matter surrounding them, for they are millions, or 

 rather millions of millions, of times too large. If, for in- 

 stance, a nebula, like the one above described as lying near 

 the southernmost Pointer, were a mass of this kind, having 

 the same mean density as the sun, and lying only at the 

 distance of the nearest of the stars from us, then not only 

 would it have the utterly monstrous dimensions stated by Sir 

 J. Herschel, but it would in the most effective way perturb the 

 whole solar system. With a diameter exceeding seven times 

 that of the orbit of Neptune, it would have a volume, and 

 therefore a mass, exceeding our sun's volume and mass 

 more than eleven millions of millions of times. But its dis- 

 tance on this assumption would be only about two hundred 

 thousand times the sun's, and its attraction reduced, as 

 compared with his, on this account only forty thousand 

 millions of times. So that its attraction on the sun and 

 on the earth would be greater than his attraction on the 

 earth, in the same degree that eleven millions are greater 

 than forty thousand or two hundred and seventy-five times. 

 The sun, despite his enormous distance from such a mass, 

 would be compelled to fall very quickly into it, unless he 

 circuited (with all his family) around it in about one-six- 

 teenth of a year, which most certainly he does not do. Nor 

 would increasing the distance at which we assume the star 

 to lie have any effect to save the sun from being thus per- 

 turbed, but the reverse. If we double for instance our esti- 

 mate of the nebula's distance, we increase eightfold our 

 estimate of its mass, while we only diminish its attraction on 

 our sun fourfold on account of increased distance ; so that 

 now its attraction on our sun would be one-fourth its former 



