OcToBER 1, 1897.] 
such questions, it is necessary to consider 
the relation of the ‘atomic weights’ to other 
magnitudes, and especially to the important 
quantity termed ‘energy.’ 
It is known that energy manifests itself 
under different forms and that one form of 
energy is quantitatively convertible into 
another form, without loss. It is also 
known that each form of energy is express- 
ible as the product of two factors, one of 
which has been termed the ‘intensity fac- 
tor,’ and the other the ‘capacity factor.’ 
Professor Ostwald, in the last edition of his 
‘Allgemeine Chemie,’ classifies some of 
these forms of energy as follows : 
Kinetic energy is the product of Mass into the 
square of velocity. 
Linear energy is the product of Length into force. 
Surface energy is the product of Surface into sur- 
face tension. 
Volume energy is the product of Volume into pres- 
sure. 
Heat energy is the product of Heat-capacity (en- 
tropy) into temperature. 
Electrical energy is the product of Electric capac- 
ity into potential. 
Chemical energy is the product of ‘ Atomic weight’ 
into affinity. 
In each statement of factors, the ‘ca- 
pacity factor’ is placed first, and the ‘ in- 
tensity-factor ’ second. 
In considering the ‘capacity factors,’ it 
is noticeable that they may be divided into 
two classes. The two first kinds of energy, 
kinetic and linear, are independent of the 
nature of the material which is subject to the 
energy. A mass of lead offers as much 
resistance to a given force, or, in other 
words, possesses aS great inertia as an 
equal mass of hydrogen. A mass of iridium, 
the densest solid, counterbalances an equal 
mass of lithium, the lightest known solid. 
On the other hand, surface energy deals 
with molecules, and not with masses. So 
does volume energy. The volume energy 
of two grammes of hydrogen, contained in 
a vessel of one litre capacity, is equal to 
SCIENCE. 
501 
that of thirty-two grammes of oxygen at 
the same temperature and contained in a 
vessel of equal size. Equal masses of tin and 
lead have not equal capacity for heat; but 
119 grammes of tin has the same capacity 
as 207 grammes of lead, that is, equal 
atomic masses have the same heat capacity. 
The quantity of electricity conveyed 
through an electrolyte under equal differ- 
ence of potential is proportional, not to the 
mass of the dissolved body, but to its equiva- 
lent, that is, to some simple fraction of its 
atomic weight. And the capacity factor of 
chemical energy is the atomic weight of the 
substance subjected to the energy. Wesee, 
therefore, that while mass or inertia are im- 
portant adjuncts of kinetic and linear en- 
ergies all other kinds of energy are con- 
nected with atomic weights, either directly 
or indirectly. 
Such considerations draw attention to 
the fact that quantity of matter (assuming 
that there exists such a carrier of properties 
as we term ‘matter’.) need not necessarily 
be measured by its inertia, or by gravita- 
tional attraction. In fact, the word ‘ mass’ 
has two totally distinct significations. Be- 
cause we adopt the convention to measure 
quantity of matter by its mass, the word 
‘mass’ has come to denote ‘quantity of 
matter.’ But it is open to anyone to meas- 
ure a quantity of matter by any other of 
its energy factors. I may, if I choose, state 
that those quantities of matter which pos- 
sess equal capacities for heat are equal, or 
that ‘equal numbers of atoms’ represent 
equal quantities of matter. Indeed, we re- 
gard the value of material as due rather to 
what it can do than to its mass; and we 
buy food, in the main, on an atomic, or, 
perhaps, a molecular basis, according to its 
content of albumen. And most articles de- 
pend for their value on the amount of food 
required by the producer or the manufac- 
turer. 
The various forms of energy may, there- 
