16 January 2021 | New Scientist | 55NIGEL
COAT
SWORTHTom Gauld
for New Scientist
Answers
Rainbow riot
I have seen many double rainbows,
but can you get triple or quadruple
ones? If so, where are the best
places to see them? What is the
maximum number that could
occur at the same time? (continued)
Nigel Coatsworth
Dudleston Heath, Shropshire, UK
What wasn’t mentioned
previously were the extra
rainbows that can appear inside
the arc of the primary bow, known
as supernumerary rainbows.
I was fortunate to glimpse one
at a Devon motorway service
station in August 2011 (pictured).
When light is reflected within
a raindrop, it is dispersed into its
constituent colours. A double
reflection, which is what creates
the primary bow, spreads the
colours out further. However,
unless the raindrops are exactly
the same size, the dispersed
patterns smear out and only
the primary one is seen.
The day that I saw a
supernumerary rainbow was
clearly an exceptional one,
where the raindrops were the
same size, so the dispersed
patterns reinforced one another
and revealed two strong bows and
a third faint supernumerary one.
I just happened to be in the
right place at the right time.
I had never seen one before
and haven’t seen one since.Guy Cox
St Albans,
New South Wales, Australia
Something that I have never
seen reported before is what I
call a “stormbow”, which seems
to be a rainbow in the salt spray
from storm waves.Going potty
If plants and trees can communicate
via their root system, do they get
lonely in pots? (continued)Nikki Walter
University of Nottingham, UK
Let’s consider the opposite of
“loneliness” in plants by thinking
about the relationships they form.
A well-known plant-bacteria
relationship is between
leguminous plants and bacteria in
their nodules. When soil is rich in
nitrogen (something that bacteria
in the nodules “fix” from the air
into a form usable to the plant),
the plant shuns the relationship
with the bacteria. You could say
that a plant only wants to make
friends when it needs something.
Plants, like most of nature, are
usually only acting in their own
interests. Keeping another tree
alive via underground fungal
networks, as trees do, benefits the
plant, as a forest is more likely to
survive than a tree on its own. Give
a potted plant what it wants and
it probably won’t get too lonely! ❚Quick quiz #84
Answers1 Hesperidium.2 To increase in size.3 Thin strands of volcanic glass,
named after the Hawaiian
goddess of volcanoes.4 Quaking aspen (Populus
tremuloides).5 The Leonids.Cryptic crossword
#48 AnswersACROSS 1 Skip, 3 Midnight,
8 Audubon, 10 Umami,
11 Prehistoric, 13 Apache,
15 On edge, 17 Resolutions,
20 Hyena, 21 Forceps,
22 Smocking, 23 HaspDOWN 1 Snap peas, 2 Indie,
4 Innate, 5 Neutron star,
6 Glanced, 7 Trig, 9 Bright spark,
12 Messes up, 14 Agree to,
16 Olefin, 18 Omega, 19 Ohms#95 Catch up^
SolutionPlayer A can be sure of winning
by starting with stack 3. At the
end of the game, the combined
heights of the towers will be 15,
so if either player reaches a
height of at least 8, they are
guaranteed to win. If A plays 3,
either B includes 5 in their first
move (by playing 1, 5 or 2, 5
or 5 alone), in which case A can
win by playing 1, 4 or 2, 4; or B
doesn’t include 5, in which case
A plays 5 next move and wins.
If A plays 1, 2, 4 or 5 as a first
move, B has a response that
can guarantee they win.