N0 . II STRUCTURE OF THE ATOM PARSON 53 



number, but also because the greater depth of the atom's envelope 

 (due to the smaller compression) makes it less likely that the mag- 

 netons will be able to maintain the most favorable attitudes. Most of 

 their action will be upon groups of eight, for which their attraction is 

 slight. Also this difficulty will increase as N (and the size of the 

 atom) increases : this is represented by the locus for the alkali metals 

 in the above diagram. For similar reasons the elements Be, Mg, Ca, 

 Sr, Ba would lie rather higher on the curve than might at first have 

 been expected. 



Now if the atoms had no envelopes, and all their magnetons were 

 in groups of eight, their volumes would be nearly (but not quite: 

 see a, below) proportional to their magneton numbers, and they 

 would lie on a straight line such as OA in the diagram. But for any 

 series of analogous elements the volume will not increase as fast as 

 N, for three reasons : 



a. Even the volume of the positive sphere proper does not increase 

 quite as fast as N, because the amount of compression due to internal 

 magnetic forces increases somewhat as N increases : this makes most 

 difference in the case of H (see §14). 



b. The expanding effect of a given number of valence magnetons 

 (§14) becomes proportionately less as N increases. The locus of the 

 atomic volumes of the elements with 8 valence magnetons will then 

 be about as I have drawn it through the minima of the curve, it being 

 assumed for simplicity (and the flatness of the minima fairly justifies 

 the assumption) that the envelope has practically disappeared in these 

 cases. There will probably be some envelope left in C and Si : hence 

 their positions. 



c. The addition of the envelope will increase the volume of a small 

 positive sphere proportionately more than that of a large one, for 

 the envelope has been assumed to be of the same " thickness " for all 

 atoms ; thus, if two spheres with radii in the ratio 1 : 2 (volumes 

 1:8) have added to each of them an envelope with a thickness equal 

 to the radius of the larger, their new radii are in the ratio 3 : 4, and 

 their volumes now 27 : 64 — a very different ratio. This effect, while 

 it is more important for H than for any other single atom, will affect 

 the series of inert elements more than any other series, for their 

 envelopes should be less compressed than those of other elements : 

 this is shown by the locus in the diagram. The actual relation in the 

 case of these elements is in excess of the prediction, for the atomic 

 volumes scarcely increase at all as N increases, that of Argon being 

 even less than that of Helium: but valence magnetons . are absent, 



