Have you ever wondered why one second is
one second long? Earth’s rotational speed
was used until 1967, when the General Con-
ference on Weights and Measures decided
that the second should be further deﬁned.
This is when cesium came into the picture.
Now the second is a multiple of the period
of cesium’s electromagnetic wave. Atomic
clocks based on this measurement miss only
one second every 1.4 million years.
SECOND TO NONE
DISCOVERY YEAR: 1860
The period of its
wave * 9,192,631,770
= 1 second
time runs on a
The white liquid you have to drink before
some X-ray procedures is a solution consist-
ing of a powder called barium sulfate and
water. It’s perfect for analyzing the gastro-
intestinal tract because X-rays won’t pass
through it. However, dissolving barium ions
in water creates a very strong poison that
causes vomiting and paralysis. Pure metallic
barium reacts violently when exposed to air,
so it’s usually preserved in oil.
A DOCTOR AT WORK,
A GANGSTER AT HOME
DISCOVERY YEAR: 1808
The next 14 elements are all similar to
lanthanum in both their properties and
application areas, which is why they (and
lanthanum) are grouped together as the
lanthanide family. Though some of the
other lanthanides are magnetic, lantha-
num isn’t. It’s used as the ﬂint in lighters,
in the lenses of mobile cameras, and as a
medication to help prevent renal failure.
THE LEADER OF THE
DISCOVERY YEAR: 1839