GETTY IMAGES X3, ALAMY ILLUSTRATION: PETER SUCHESKIF
or over 200 years, the kilogram has been the
international standard unit of mass. Yet its name
suggests there was once another standard, which was
1,000 times lighter: the gram. Chosen by a panel of
distinguished French academics in 1791, this was
originally defined as the mass of one cubic centimetre of
distilled water at 4°C. This is the temperature at which
water reaches its maximum density, thus giving a cubic
centimetre of the stuff its greatest possible mass. While
scientifically neat and tidy, the mass of a gram was still
pretty small – barely as much as an almond – and it was
quickly criticised as impractical for commercial use. So
in 1799, the French republic adopted the kilogram,
defined via the mass of a platinum weight – the
approach still used until 2018, when it was finally
replaced by a far more sophisticated definition.U
ntil recently, concern that electronic emissions from laptops,
e-readers and phones could interfere with aircraft systems
led to passengers being asked to put such devices into low-
emission ‘flight mode’ during take-off and landing. In recent
years, these restrictions have been eased, but they still apply to
phones. That’s because the aerospace industry believes that
radio emissions from phones still have the potential to cause
interference – and are suspected to have sometimes affected
headphones used by pilots.Is there any point to turning my phone
to ‘flight mode’ on a plane?
Joanne Harris, LynwoodHow did we decide
how heavy a gram is?
Timothy Evans, VanderbijlparkWas maths invented or
discovered?
Lee Robinson, Johannesburg NorthGETTY X2T
he fact that one plus one equals
two, or that there’s an infinite
number of primes, are truths about
reality that held even before
mathematicians knew about them. As
such, they’re discoveries – but they were
made using techniques invented by
mathematicians. For example, according
to Pythagoras’ theorem, the square of
the hypotenuse of a right-angled triangle
is equal to the sum of the squares of the
other two sides. This is true for all
right-angled triangles on a level surface,
so it’s a discovery. Showing it is true,
however, requires the invention of a
proof. And over the centuries,
mathematicians have devised hundreds
of different techniques capable of
proving the theorem. In short, maths is
both invented and discovered.A Most lipsticks
contain fish scales.
A If they stop
swimming, sharks will
sink to the bottom of
the sea, as they have
no air bladder for
buoyancy.
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&
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