F. W. Very — Nebulosity around Nova Persei. 57 



Laving masses in the ratio of 4 : 2 : 1, and, if so, bear witness to 

 the existence of at least three sorts of ions out of which, in 

 varying proportions, we may conceive the atoms to be made. 



An alternative hypothesis assumes that there are as many 

 kinds of ions as of atoms, and that the difference between a 

 corpuscle and an atom of the same substance is principally one 

 of size. If so, since the atomic weights of hydrogen and helium 

 are as 1 to 4, if the masses of their corpuscles have the same 

 ratio, the outer arc might be composed of hydrogen corpuscles, 

 the inner ring of helium corpuscles, and the central member of 

 the series, that is, what we call the " outer ring," would consist 

 of corpuscles belonging to an unknown substance with atomic 

 weight of two. A single good spectroscopic observation, such 

 as might possibly be obtained with an objective prism of large 

 size, would be of inestimable value in deciding this and other 

 questions raised by this extraordinary object, whose like may 

 not be seen again for many years. "^ 



A selection between these hypotheses will be a matter of 

 opinion. Seeing that the chemical elements exhibit many 

 properties analogous to those of homologous series in hydrocar- 

 bons, I am inclined to favor the supposition that the atoms are 

 formed by various arrangements of numerous ions of perhaps 

 only three species. Even when their motions are confined and 

 limited in the ionic aggregate (the atom), three fundamental 

 sorts of ionic motions are distinguishable in principal, first 

 subordinate, and second subordinate series of spectral lines, 

 whose pressure shifts, according to Dr. W. J. Rumphreys,f 

 are in the ratio 1:2:4. The same sequence appears again in 



* Note added April, 1903. — Since this paper was read at tlie annual meet- 

 ing of the Astronomical and Astrophysical Society of America, in Washing- 

 ton, December, 1902, Professor Perrine has published the following measure- 

 ment, made with a slit-spectrograph of special construction, provided with a 

 quartz prism and quartz lenses: "The slit of the spectrograph was placed 

 across the brightest portion of condensation D. The resulting negative 

 showed a very faint spectrum, which, after careful consideration and some 

 experiments was deemed to be that of the nebulosity. So far as can be told 

 from such small dispersion and intensity, the spectrum is continuous, with 

 the greater portion of the light condensed in a band between H« and Hy 

 This band is strongest just above H^ and from this point fades gradually 

 until it is entirely lost in the H and K calcium region. Beyond this point, 

 up to the ultra-violet region, there is a very slight increase of strength again. 

 It is suspected that in one or two cases there may be traces of bright lines, 

 but the whole spectrum is so faint as to preclude any definite deduction on 

 this i3oint. The above observation shows that the spectrum of this mass of 

 nebulosity is not the ordinary bright-line spectrum of the nebulae." (Publi- 

 cations of the Astronomical Society of the Pacific, XY, No. 88, p. 26, 1903.) 

 This observation is not inconsistent with the supposition that a spectrum, 

 normally composed of bright lines, has been extended and diffused by 

 excessive motion of the radiating particles through a considerable range of 

 velocities, according to Doppler's principle, until the resulting spectrum is 

 one of ill-defined, superposed, hazy bands. 



f Astrophysical Journal, vi, 219, 1897. 



