500 
with this fragment of regularity that he- 
lium and argon show a greater difference. 
Then, again, sodium, the middle element of 
the lithium triad, is very similar in proper- 
ties both to lithium and potassium ; and we 
might, therefore, expect that the unknown 
element of the helium series should closely 
resemble both helium and argon. 
Leaving now the consideration of the 
new element, let us turn our attention to 
the more general question of the atomic 
weight of argon, and its anomalous posi- 
tion in the periodic scheme of the elements. 
The apparent difficulty is this: The atomic 
weight of argon is 40; it has no power to 
form compounds, and thus possesses no 
valency ; it must follow chlorine in the 
periodic table, and precede potassium ; but 
its atomic weight is greater than that of 
potassium, whereas it is generally contended 
that the elements should follow each other 
in the order of their atomic weights. If 
this contention is correct, argon should 
have an atomic weight smaller than 40. 
Let us examine this contention. Taking 
the first row of elements, we have: 
li=7, Be—9.8, B= 11, C=12, N=14, O16, 
F=19, ?=20. 
The differences are: 
2.8, 1.2, 1.0, 2.0, 2.0, 3.0, 1.0. 
It is obvious that they are irregular. 
The next row shows similar irregularities. 
Thus: 
(?2=20), Na=23, Mg=24.3, Al=27, Si=28, P=31, 
S =32, Cl=35.5, A=40. 
And the differences : 
3.0, 1.3, 2.7, 1.0, 3.0, 1.0, 3.5, 4.5. 
The same irregularity might be illus- 
trated by a consideration of each succeed- 
ing row. Between argon and the next in 
order, potassium, there is a difference of 
—0.9; that is to say, argon has a higher 
atomic weight than potassium by 0.9 unit ; 
whereas it might be expected to have a 
lower one, seeing that potassium follows 
SCIENCE. 
[N. S. Von. VI. No. 144. 
argonin thetable. Farther on in the table 
there is a similar discrepancy. The row is 
as follows : 
Ag=108, Cd=112, In=114,Sn—119, Sb —120.5, 
Te=127.7, I=127. 
The differences are: 
4.0, 2.0, 5.0, 1.5, 7.2, —0.7. 
Here, again, there is a negative difference 
between tellurium and iodine. And this 
apparent discrepancy has lead to many and 
careful redeterminations of the atomic 
weight of tellurium. Professor Brauner, in- 
deed, has submitted tellurium to methodical 
fractionation, with no positive results. All 
the recent determinations of its atomic 
weight give practically the same number, 
127.7. 
Again, there have been almost innumer- 
able attempts to reduce the differences be- 
tween the atomic weights to regularity, by 
contriving some formula which will express 
the numbers which represent the atomic 
weights, with all theirirregularities. Need- 
less to say, such attempts have in no case 
been successful. Apparent success is al- 
ways attained at the expense of accuracy, 
and the numbers reproduced are not those 
accepted as the true atomic weights. Such 
attempts, in my opinion, are futile. Still, 
the human mind does not rest contented in 
merely chronicling such an irregularity ; it 
strives to understand why such an irregu- 
larity should exist. And, in connection 
with this, there are two matters which call 
for our consideration. These are: Does some 
circumstance modify these ‘combining pro- 
portions’ which we term ‘atomic weights ’? 
And is there any reason to suppose that 
we can modify them at our will? Are 
they true ‘ constants of Nature’ unchange- 
able, and once for all determined? Or are 
they constant merely so long as other cir- 
cumstances, a changein which would modify 
them, remain unchanged. 
In order to understand the real scope of 
