500 



NATURE 



[June 17, 1920 



Our Astronomical Column. 



The Masses of the Stars. — The mass of a star 

 is perhaps its most important element, but it is one 

 that can be ascertained only in exceptional cases. 

 Prof. H. N. Russell, in a paper read at the twenty- 

 first meeting of the American Astronomical Society, 

 gathered together all the evidence, direct and indirect, 

 on the subject, grouping the results by spectral type. 



Method I. is the usual one for visual binaries the 

 orbits and parallaxes of which are known; Method II. 

 is similar, where the parallax and relative motion, 

 but not the orbit, are Icnown ; Method III. is from 

 spectroscopic binaries where both spectra are shown, 

 a mean inclination being assumed; and Method IV-, 

 the vaguest of all, derives the parallaxes of binaries 

 from their proper motions. 



The resulting mean masses for the pairs of stars 

 are : — 



Spectrum I. II. IH. IV. 



B„-B, — IO-4 17-5 7-1 



Bg-A, 59 30 40 8-4 



^M } «=-' { = = ^-' ^8 



F-F, I ( 3-5 3-4 — 2-5 



Fg-K, \ dwarf \ i-8 1-4 — 07 



K,-M J I 0-7 i-o — — 



, The Sim's mass is taken as i. 



The following formulae are given for the hypo- 

 thetical parallax (h) of systems of mean distance a, 



and period '? -. h=f—\ or where s is the apparent 



distance and w the apparent relative motion, in 

 seconds of arc p^er annum, ^ = 0409/5 ^T^i 



The constant / has the value 050 for all giant stars, 

 058 for dwarfs of spectrum A, 0-72 spectrum F, 086 

 spectrum G, 100 spectrum K, and 1-14 spectrum M. 

 The probable error is given as 12 per cent, where the 

 first formula can be used, and as 22 per cent, in other 

 cases. 



The Planet Jupiter.— The Rev. T. E. R. Phillips, 

 director of the Jupiter section of the British Astro- 

 nomical Association, contributes an interesting article 

 on the planet to the June number of Sdentia. After 

 giving a rdsumd of Jovian phenomena during the last 

 twenty years, including the ,red spot and the south 

 tropical disturbance, Mr. Phillips notes the startling 

 change in the aspect of the planet which took place 

 early in 1919; the disturbance and the red-spot hollow 

 both practically disappeared, though the spot itself 

 survived. Discussing the physical condition of 

 Jupiter, he notes the similarity to the sun in density, 

 in varying rotation periods according to latitude, and 

 in the dark belts which are comparable with the spot 

 zones. He suggests that the red spot may indicate a 

 vast cyclonic movement in the atmosphere, noting 

 that this view would explain the rapid passage of the 

 dark matter of the tropical disturbance tound the 

 spot when the two are in conjunction. He notes, in 

 conclusion, the importance of Jovian study from the 

 point of view of cosmogony, since it illustrates a stage 

 intermediate between the solar condition and the 

 earliest geological periods. 



Parallax Work at the Sproul Observatory. — The 

 list of stars with known parallaxes is being rapidly 

 extended, thanks to the extensive organised campaign 

 carried on by many observatories which possess large 

 equatorials. " Dr. Miller, of the Sproul Observatory, 

 has published a useful list of fifty observed parallaxes 

 (Proc. Amer. Phil. Soc, vol. lix., No. 2). Five stars 

 on the list have parallaxes above 01", viz. W.B. (i) V. 

 592 = o-i46'', 9 Argus = o-i2i'', i Persei=o-i2o", Lalande 

 17161=0-104", and W.B. (i) IV. 1189 + 0-103". The 



NO. 2642, VOL. 105] 



values found for 7* and y" Andromedae are 0021* and 

 0005" ; those for the preceding and following com- 

 ponents of the wide pair 16 Cygni are +0037" and 

 + 0018". In each of these systems the true parallaxes- 

 of the components are presumably the same. The 

 discordances are a measure of the probable errors, 

 which in each case are of the order of 001". 



An interesting feature is the closeness with which' 

 the new figures verify many of Prof. H. N. Russell's 

 hypothetical parallaxes, deduced from assumptions 

 regarding the masses of binaries. 



Nuclear Constitution of Atoms.^ 



By Sir Ernest Rutherford, F.R.S. 



'T^^'HE idea of the nuclear constitution of atoms was 

 -*- developed frotn an examination of the scattering 

 of swift a-particles in passing through matter, and 

 the advance afterwards made was due to the proof 

 by Moseley of the close connection between the atomic 

 number of an element and the nuclear charge. The 

 accurate determination of the nuclear charge is of 

 prime importance. Recent unpublished experiments, 

 by Mr. Chadwick in the Cavendish Laboratory 

 indicate that the nuclear charge on an atom in funda- 

 mental units is eaual to the atomic number within 

 an accuracy of about i per cent. It follows that 

 there is a region surrounding the nucleus where the 

 law of the inverse square holds accurately. The 

 problem of the constitution of the atom divides itself 

 naturally into two parts : one the arrangement of 

 the external electrons on which the ordinary chemical 

 and physical properties of the atom depend, and the 

 other the constitution of the nucleus on which depend 

 the mass of the element, the possibility of isotopes, 

 and radio-activity. The nucleus is composed of posi- 

 tively charged units and negative electrons in very 

 close combination, and estimates of its dimensions 

 are possible from a study of the collision of o-particles 

 with light atoms. Close to the nucleus there is a 

 rapid change in the magnitude and direction of the 

 forces, probably in part connected with the deforma- 

 tion of the nucleus structure under the intense forces 

 which arise in a close collision. 



Unless the nuclei are very stable, it is to be antici- 

 pated that they would be deformed, and possibly 

 broken up, as a result of a direct collision with swift 

 a-particles. In previous experiments evidence was 

 given that long-range particles resembling hydrogen 

 atoms were liberated by the passage of a-particles 

 through pure nitrogen. ' New experiments have been 

 made to 'determine by a modified method the nature 

 of these particles bv bending them in a magnetic 

 field. The amount' of deflection of the particles 

 liberated from the nitrogen of the air was shown to 

 be the same as for H atoms arising from a mixture 

 of hydrogen and carbon dioxide. This showed 

 definitelv that hydrogen is one of the products of the 

 disintegration of the nitrogen atom, and is one of the 

 original components of the nitrogen nucleus. The 

 possibility' that the long-range particles are atoms of 

 mass 2, 3, or 4 carrying a single charge may be 

 definitely excluded. 



The deflection in a magnetic field of the short-range 

 particles which are liberated from nitrogen and 

 oxygen, and were originally assumed to be recoil 

 atoms of these elements, is not only much greater 

 than that to be expected for such recoil atoms, but 

 is also greater than the a-particle but less than the 

 H atoms liberated from a mixture of hydrogen and 

 carbon dioxide. 



1 Synopsis of the Bakerian Lecture delivered before the Royal Society on 

 June 3. 



