440 O. A. Derby—Occurrence of Gold in Brazil. 
is actively registering the time element in vital phenomena 
through the rate of nervous transmission, the rate of muscular 
contraction, the duration of optical and auditory impressions 
et cetera; and we cannot ignore the fact that all the great 
living theories of the present, contain the time element as an 
essential part. Now may it not be that the reason why chemis- 
try hasevolved no great dynamical theory, that the word affinity 
has disappeared from our books, and that we go on accumu- 
lating facts in all directions but one, and fail to draw any 
large generalization which shall include them all, is just because 
we have made so little use of the fundamental concept, time. 
To expect to draw a theory of chemical phenomena from the 
study of electrical decompositions and of thermo-chemical data, 
or from even millions of the customary static chemical equa- 
tions would be like hoping to learn the nature of gravitation by 
laboriously weighing every moving object on the earth’s surface 
and recording the foot-pounds of energy given out when it fell. 
The simplest quantitative measure of gravity, is, as every one 
knows, to determine it as the acceleration of a velocity; when 
we know the value of g we are forever relieved in the problem 
of falling bodies from the neéessity of weighing heterogeneous 
objects at the earth’s surface, for they will all experience the 
same acceleration ; may there not be something like this gran 
simplification to be discovered for chemical changes also’ 
The study of the speed of reactions has but just begun; It 18 
a line of work surrounded with unusual difficulties, but I cont- 
dently believe it contains a rich store of promise; all other means 
for measuring the energies of chemism seem to have been tri 
except this; is it not therefore an encouraging fact that to us, 
the chemists of the nineteenth century, is left for exploration 
the great fruitful field of the true dynamics of the atom, the 
discovery of a time rate for the attractions due to affinity. 
kinds of changes in reference to their velocity ; the physiologist 
h n 
Art. LIV.—Peculiar Modes of Occurrence of Gold in Brazil ; 
by OrvitteE A. DERBY. — 
1. NATURAL DEPOSITION OF GOLD FROM SOLUTION. 
Tue following facts are believed to justify the heading of this 
paragraph. A specimen (Mus. No. 84) in the National Mu- 
seum at Rio de Janeiro shows films of gold which are difficult 
to account for on any other hypothesis. The specimen W 
received some thirty years ago from the Danish Collector 
Claussen, with the indication “gold on limonite, Ponte Grande, 
Sabara, province of Minas Geraes.” The formation at this 
