No} 
ON 
The real significance ef recent developments is in the fact that they 
change—in a way revolutionize—some of our ideas of things. And here 
let me say that proven facts and proposed theories should not be confused. 
A theory is simply a working hypothesis, invented for the purpose of ex- 
plaining facts, to be discarded when facts are discovered with which the 
theory is not in harmony. A theory may explain many facts, it may be 
generally accepted, it may have survived for generations and be false. 
The phlogiston theory, the corpuscular theory are two examples. Shall 
we say that the theory of the indestructibility of matter and of the con- 
servation of energy are two others? 
The usual chemistry text-book would have us believe in the inde- 
structibility of matter because the chemist can change the form of matter 
almost at will, and in all the chemical reactions there is no loss of weight. 
In replying to this argument I wish to make three points. 
First. The balance, notwithstanding the statement of text-books, com- 
pares weights and not masses, and it is only because weight is assumed 
to be proportional to mass that we say we determine mass by the balance. 
What we really compare is the gravitational force which the earth exerts 
on two masses, and we have no a priori right to assume that this gravita- 
tional force is absolutely independent of the state or molecular arrange- 
ment of the attracted body. Why, for instance should we expect an abso- 
lutely uniform field of force about a crystal when that same crystal will, 
if placed in a proper solution, continue to grow symmetrically, and perhaps 
replace a broken-off corner before beginning its growth? 
It is conceivable that there shoula be a loss of weight in chemical re- 
actions and yet no destruction of matter. It is possible that mass and 
weight are not strictly proportional. if J. J. Thomson were not disposed 
to question the equation w—=m.g he would: not have experimented with a 
pendulum of radium, and he would not now be experimenting with a pen- 
dulum of uranium oxide. 
In the second place there is an apparent change of weight in chemical 
reactions as has been shown by several experimenters, notably by Landolt,’ 
who found a loss in forty-two out of fifty-four cases. The chemical reac- 
tions were brought about in sealed glass tubes which generally weighed 
less after the reactions than they weighed before. Later® it was found 
that some of these losses might be attributed to temperature and yolume 
1H{. Landolt. Preuss. Akad. Wiss. Berlin, Sitz. Ber. 8, pp. 266-298, 1906. 
2Landolt. Preuss. Akad. Wiss. Berlin, Sitz. Ber. 96, pp. 354-587, 1 
