348 
throughout those depths within which 
change of temperature with depth is the 
marked feature of the temperature distribu- 
tion. In other words, if, for example, we 
consider the Kelvin earth, the strata above 
.035 of earth radius will be strata of smaller 
conduction than the surface strata. From 
the surface downward as far as .035 radius, 
conduction will decrease to a minimum. 
Below this, conduction will increase again, 
due to preponderating pressure, finally to 
exceed the surface value. But the com- 
puted temperature distribution of Kelvin’s 
earth is such that at .035 radius the initial 
temperature excess of 3,900° has been 
reached to within one or two percent. Be- 
low this in depth Perry’s correction will be- 
gin to apply, but the further changes of 
temperature are so nearly negligible that 
the consideration of conduction is superflu- 
ous. From this point of view, therefore, 
the staggering force of Perry’s clever argu- 
ment is removed. Of course, I am fully 
aware that an argument from the supposed 
parallelism of physical properties of a given 
body (in the present case heat conduction 
and viscosity) is not inevitably convincing; 
but in physical geology, for some time to 
come I dare say, the question will be; not 
one of rigorous proof, but rather one of form- 
ing a rational opinion. 
In passing I will indicate the importance 
of an increased knowledge of the isometrics 
of liquid and solid matter, relations which 
have thus far been found simpler in charac- 
ter than other thermo-dynamic properties 
as I shall again point out in the course of 
the address. 
I want finally to add a few words on the 
electro-chemistry of magmas. The physical 
chemistry of molten rock has already been 
somewhat extensively considered, but I am 
hardly competent to review it. In this 
country, Joseph Iddings and, more recently, 
George F. Becker have discussed the 
natural differentiation of magmas from dif- 
SCIENCE. 
[N. 8. Von. VI. No. 140. 
ferent points of view. Here I will merely 
include certain pyrometrie experiments on 
the electric conduction of fused glasses 
which seem to give promise of throwing 
light on the chemical constitution of com- 
plex silicates and to be suggestive in other 
ways. Insuch measurements, if the magma 
is made to pass from the solid to the liquid 
state, the observed electric conduction con- 
tains no evidence either of a melting point or 
of polymerism. The law of thermal varia- 
tion is easily derived and it agrees closely 
with the corresponding behavior of a zine 
sulphate solution, for instance, observed 
through a range of temperature. In a 
general way, electric resistance decreases in 
geometric progression when temperature in- 
creases in arithmetical progression. Con- 
sidered relatively to the composition of the 
magmas, electric conduction shows a 
marked and regular increase with the de- 
gree of theacidity of the magmas. The less 
fusible acid magmas are better conductors. 
than the basic magmas at the same tempera- 
ture. Curiously enough, conduction thus 
runs in an opposite direction to fusibility. 
However viscous a magma may be, there- 
fore, and however cogent the arguments, 
such as those launched by Becker against 
the differentiating importance of ordinary 
diffusion may prove, it is fair to conclude 
that a thorough change of chemical struc- 
ture through ionic diffusion, whether di- 
rected by an electric field or otherwise, 
must be an easy possibility fora sufficiently 
hot but otherwise solid magma. The re- 
sults point specifically to the desirability of 
repeating Hittorf’s brilliant experiments on 
the migration of the ions for a silicious 
medium. This ought not to be difficult, 
seeing that such a menstrum need not even 
be liquid to be compatible with a high or- 
der of electric conduction. 
Further consideration of the subject 
shows the probable passage of conduction 
through a maximum when acidity is con- 
