54 | New Scientist | 22 June 2019
Heated windshield
It is a windy -20°C outside
and I just saw a flock of ducks
fly over. How do the birds stop
their eyeballs freezing?The Royal Society for the
Protection of Birds, via Twitter
Blood vessels provide the eyes
with a continuous supply of blood,
which ensures constant warmth
and prevents them from freezing.Richard Lucas
Camberley, Surrey, UK
There are a number of features
that combine to protect the
eyes of ducks – and most other
animals – from freezing. The eyes
themselves and the tears that
cover them are quite salty and so
won’t freeze until the temperature
drops quite a long way.
In addition, the eyes are mostly
surrounded by nice warm flesh
as well as bone with its good blood
supply, both of which serve to
maintain their temperature. And
in many animals, ducks included,
the eyes have a third eyelid, or
nictitating membrane, that has
its own blood supply and a gland
that secretes tears high in lipids
that confer extra protection.Mike Follows
Sutton Coldfield, West Midlands, UK
Birds’ eyes are recessed into
their warm heads. And in cold
surroundings, the body diverts
blood to the brain and other vital
organs. Besides, a flying bird will
generate a lot of heat during flight.
The fluid inside birds’ and
other animals’ eyes, the aqueous
and vitreous humours, provides
a fair amount of heat capacity,
so that it will tend to match
the core body temperature.
The corneal tissue at the front
of the eye has high thermal
conductivity so it doesn’t stray too
far from body temperature even
when the ambient temperature
is extreme. For example, if the
environment is at -11°C, the surface
temperature of a human cornea
only falls to 28.6°C.
Birds flying in a group take it inturns to go at the front and, when
they are slipstreaming, probably
experience a reduced headwind
and smaller windchill as a result.
They will also blink to ensure their
eyes don’t dry out, ensuring they
stay covered in a film of salty fluid
that acts like antifreeze.
There is an example of human
eyes failing to freeze in windy
and extremely cold surroundings.
On 10 June 1990, a window on
the flight deck of a BAC-111
aircraft failed and the sudden
decompression pulled the captain
head first through the breach.
A quick-thinking flight attendant,
Nigel Ogden, grabbed his legs and
saved his life. Ogden ended up
with a frostbitten cornea, but his
eyes didn’t freeze, although it
would have been extremely cold.Tim Coxsen
Glenden, Queensland, Australia
They adopt the “safety squint”
technique. Like when you
use an angle grinder without
eye protection...We are but dust
What is dust? What is it made of,
and is it bad for human health?Dee Dhamija
London, UK
Dust includes tiny particles of
debris and dead skin. Its small
size means it can be inhaled and
potentially evoke an immune
reaction. Such allergic reactions
may be minor or major depending
on the individual. Dust can also
serve as a “fomite”, potentially
carrying viruses and possibly
passing on infections.Charles Harrison
Health and safety adviser
Willand, Devon, UK
Household dust is mostly made
up of human skin, microscopiccreatures and dead bugs. This may
make your skin crawl, but doesn’t
offer significant health risks for
most people.
However, other forms of dust
can be very harmful indeed.
Last year, tiny particles of sand,
wood and asbestos contributed
to 12,000 deaths from lung
disease in the UK, according to
the Health and Safety Executive.
Many more deaths will have
been caused by exposure outside
the workplace, including to
particulates produced by cars.
Repeated, long-term exposure
to high levels of dust of any form
can harm your health. Normal
household exposure will probably
not cause you any problems, but
working in a dusty environment
may well do so.
Excellent advice is available
from the Health and Safety
Executive or the US Occupational
Safety and Health Administration.
If dust in the air reaches a high-
enough level, it can also cause
explosions – which are certainly
harmful to health!Eva Kumar
National Institute for Health
and Welfare, Kuopio, Finland
In a recent study I was involved
in, we looked at levels of
brominated and phosphorous
flame retardants in dust in
children’s bedrooms in Finland
(Chemosphere, doi.org/c68h).
We found several flame
retardants, which are added
to household and consumer
products, but not at levels
considered to be damaging
to health. We also discovered
that, in indoor environments,
dust is a major contributor to
human exposure to these
flame retardants. ❚This week’s new questions
Galactic traveller My wife told me I should get out more.
I replied that I am just about to celebrate my 66th free trip
around the sun. Can anyone tell me how far I have travelled
in our galaxy during that time? Stephen Dowsett, London, UKLucky dip Which gives me better odds of winning the
lottery: buying one ticket a week or 52 tickets once a year?
John Clark, Leeds, UKWant to send us a question or answer?
Email us at [email protected]
Questions should be about everyday science phenomena
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CAVAN^ I
MAGES/
PL
AINPICTUREHow far through the
galaxy can one person
travel during their life?