Ppa) a UTAH ACADEMY OF SCIENCES 107 
THE ATOMIC THEORY AND THE ATOM. 
BY W. D. BONNER. 
The atomic theory had its inception, apparently, a- 
mong the early Greek philosophers. Thus Thales, Anax- 
imines and Heraclitus, all of whom lived during the sixth 
century B. C., argued that all material things are built 
up from one fundamental substance. Each one, of course, 
chose a different thing to serve as his primitive element, 
water, air, and fire, respectively, and each chose poorly. 
In the 5th century B. C., Democritus clearly stated that 
all things are made up from a primitive element, and that 
this element is made up of the smallest particles possible, 
the atoms; that these atoms differ from each other in form 
and size, but are all of identical composition and that 
they all are in a state of continuous motion. Slight vari- 
ations on this theme, such as changing the number of 
primitive materials, and makng new selections for them, 
was the only progress made in developing a theory of the 
composition of-matter, until the 19th century A. D. In 
1803, John Dalton attempted to formulate a quantitative 
hypothesis regarding the composition of substances, as 
opposed to the purely qualitative speculation which had 
been indulged in up to that time. He had, for a found- 
ation, the knowledge of a considerable number of the 
chemical elements, as we now call them; he knew that 
the great number of individual substances are made up of 
these numerically few elements, and also, the Law of 
Definite Proportion was, by this time, fairly well es- 
tablished. The first question, then, which he asked him- 
self was, are the atoms of the elements all exactly alike, 
or are they only similar? If they are the latter, then it 
is reasonable to believe that one should be able to pre- 
pare samples of the same pure substance differing slightly 
from each other, just as one can separate fine sugar crys- 
