372 Lf. A. Hill—Notes on Argon and Helium. 
We seem now, however, to be approaching an era of greater 
light, and F fully’ believe that the next few years will be pro- 
ductive of great advances in chemical and physical knowledge. 
I cannot now go into the subject of classification, but I will in 
conclusion refer to a closely related subject. In my previous 
article it will be remembered I called attention to a very regu- 
lar alternation of intervals of 3 and 1 in the natural series ot 
the elements, and in the table at page 416 of the May number 
of this Journal will be found a number of terms of the series 
so formed, not corresponding to known elements, which may 
possibly represent elements as yet unknown. It is remarkable 
that so many of those who have been giving their attention to 
the intricate subject of chemical classification have, by entirely 
different processes of reasoning, arrived independently at the 
common conclusion; that there are still a number of undis- 
covered elements, particularly in what may be termed the 
eighth or transitional family of Mendeléeff ; and furthermore 
that they have so closely agreed on the atomic weights of the 
same. Of the various classifications thus far cited in connec 
tion with the discoveries of argon and helium, perhaps the 
most mature are those of Mr. C. J. Reed and M. Lecog de 
Boisbaudran. When several investigators, working thus inde- 
pendently, and from data which though at times overlapping 
so to speak, yet are in the main different, or at any rate lead to 
different theories and systems of classification ; when I say, in 
such cases, practically the same conclusions are arrived at, 
these results should naturally command a respectful considera- 
tion; and that is precisely what seems to have happened in 
the present case. 
I can bring this out most clearly, I think, in tabular form, 
comparing some of the terms of the series referred to with the 
elements predicted by other classifications, ete. 
1 2 a et 5 6 8 9 
hie v4 ali re et ee et | 
= BS x Shae e el ake gi 
a g eS) d 2 ga Sw g 
< SSS 8 Ve) eee ee sm | & 
S| Sa pe eiees o mE a fea a 
= oS gol Oe ay ; 2 2 
2 sa (Soe) {Bo 9 |) See 
ca 4 S |A ns Ca Diving 5 
Pic eSB MEO 
helium?= 4| 3:9 4 5 9) 4°26 4 
argon = 20) 20°0945 20 | 20 20 20 20 20 
= 36| 36°40+°08| 36 37 36 136 to 89; A=40 ?| 36 
2 Sion 68 62 
? = 83) 84-00 220) 64 82 83 82 84 
Pe = anG 116 Note A 
2 Sas eee ae ee 129-130 132 
