ries are directly attributed to
scientists working under the Atomic Energy Commission at the University
of California's Radiation Laboratory at Berkeley.

But it is apparent that our present knowledge of the elements stretches
back into history: back to England's Ernest Rutherford, who in 1919
proved that, occasionally, when an alpha particle from radium strikes a
nitrogen atom, either a proton or a hydrogen nucleus is ejected; to the
Dane Niels Bohr and his 1913 idea of electron orbits; to a once unknown
Swiss patent clerk, Albert Einstein, and his now famous theories; to
Poland's Marie Curie who, in 1898, with her French husband Pierre
laboriously isolated polonium and radium; back to the French scientist
H. A. Becquerel, who first discovered something he called a "spontaneous
emission of penetrating rays from certain salts of uranium"; to the
German physicist W. K. Roentgen and his discovery of x rays in 1895; and
back still further.

During this passage of scientific history, the very idea of "element"
has undergone several great changes.

The early Greeks suggested earth, air, fire, and water as being the
essential material from which all others were made. Aristotle considered
these as being combinations of four properties: hot, cold, dry, and
moist (see Fig. 1).

[Illustration: Fig. 1. The elements as proposed by the early Greeks.]

Later, a fifth "essence," ether, the building material of the heavenly
bodies was added.

Paracelsus (1493-1541) introduced the three alchemical symbols salt,
sulfur, and mercury. Sulfur was the principle of combustability, salt
the fixed part left after burning (calcination), and mercury the
essential part of all metals. For example, gold and silver were
supposedly different combinations of sulfur and mercury.

Robert Boyle in his "Sceptical Chymist" (1661) first defined the word
element in the sense which it retained until the discovery of
radioactivity (1896), namely, a form of matter that could not be split
into simpler forms.

The first discovery of a true element in historical time was that of
phosphorus by Dr. Brand of Hamburg, in 1669. Brand kept his process
secret, but, as in modern times, knowledge of the element's existence
was sufficient to let others, like Kunkel and Boyle in England, succeed
independently in isolating it shortly afterward.

As in our atomic age, a delicate balance was made between the
"light-giving" (desirable) and "heat-giving" (feared) powers