Lucky mark
Question: Local birds tend to eat little black insects. So how come they void
themselves on me from a great height with a white and annoyingly conspicuous
product?
(continued)
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Answer: Your previous correspondents omit one fact, oviparity. The evolution
of insoluble excreta has nothing to do with a 鈥済ood power-to-weight ratio鈥� or
the ability to 鈥渓ive in ecological niches where water is scarce鈥�.
It evolved because all birds and many reptiles begin their life inside an
egg. Even heavy egg-laying amniotes that live in water as adults, such as
penguins and crocodiles, must survive this early phase without poisoning their
shelled enclosure with any water-soluble metabolites.
脰rn贸flur Thorlacius
Reykjavik, Iceland
Long hours
Question: Do all points on the Earth receive an equal number of daylight
hours over the course of a year?
I realise that the intensity of the Sun鈥檚 rays will differ considerably
depending on your latitude, but does a person living in Alaska see the Sun for
as long as somebody living in Ecuador over the course of a year?
Answer: The short answer is that all points on the globe do receive the same
amount of sunlight, because any portion of the Earth that points towards the Sun
in summer will point away in winter, so the extra daylight in summer precisely
cancels the lack of daylight in winter. However, this is true only for a simple
spherical body in a circular orbit about the Sun.
First, the orbit of the Earth is not circular. According to Kepler鈥檚 third
law, the Earth travels faster when it is closer to the Sun than when it is
farther away.
Because the Earth is closest to the Sun in early January, it moves fastest
during the northern hemisphere鈥檚 winter months. This can be seen by the fact
that the time from the autumn to the spring equinox is about three days shorter
than the time from the spring to the autumn equinox.
Because the Earth has more daylight during the northern hemisphere鈥檚 summer
and spends more time on the 鈥渟ummer side鈥� of the equinoxes, the northern
hemisphere receives slightly more daylight than the southern. This amounts to
about six hours of additional daylight per year at 50掳 North, with higher
latitudes receiving even more daylight.
The second major effect is the refraction of sunlight by the atmosphere.
Because of this, we can still see the Sun after it has sunk below the horizon.
Typically, sunset appears to happen when the Sun is actually about half a degree
below the horizon. Along the equator, the difference amounts to about 4 minutes
per day when daylight is more than 50 per cent of the day.
While this gives some extra daylight to everyone wherever they live, it gives
more daylight in areas where the path of the Sun makes a shallow angle with the
horizon.
The shallow angle means that it takes longer to reach half a degree below the
horizon. So higher latitudes (both north and south) get the most additional
daylight. At 50掳 latitude, it is up to 8 minutes longer per day when
daylight is more than 50 per cent of the day鈥攐r about 36 hours per year on
average.
Barry Spletzer
Albuquerque, New Mexico
Title claims
Question: It is easier to read titles on book spines on my bookshelf if I
incline my head, why?
(continued)
Answer: In response to the additional query to this question (why are book
spines printed in third angle projection?) this is because book titles are
usually printed running down the spine, so that when you lay a book flat on your
coffee table both the front cover and the spine are readable. It seems the
logical thing to do. Publishers鈥� marketing departments also insist on it if they
are wise. When books are piled up on booksellers鈥� display counters, customers
can read the titles from at least two angles.
Hugh Newbury
by e-mail, no address supplied.
Answer: I understand that the titles on book spines are printed in third
angle projection so that books stacked horizontally (which can be read without
tilting the head in any direction) can be arranged with the front cover
uppermost.
In 鈥渇irst angle projection鈥� the books must be arranged with the front cover
face down. The exact reasoning for the orientation is probably a marketing
strategy鈥攁 deduction supported by the fact that all books in my possession
from publishers in the US have spines titled in third angle projection, as have
all paperbacks, age and origin notwithstanding.
British publishers have changed the orientation of their titles in recent
years from mostly first angle to third angle projection. This seems to have
occurred mainly in the past 10 years鈥擨 have a few books dated 1988 with
the first angle projection, though none more recent than this.
Oddly, despite being aware of the reasoning behind the third angle
orientation, which also applies to the spines of pre-recorded video cases, audio
cassettes and CDs, when I hand- label a cassette I always do it in first angle
mode鈥攅ven when I do the labelling flat before sticking the label to the
case. If anyone can explain that, I鈥檇 be interested.
Julian White
London
This week鈥檚 questions
In a flap: What are those little flaps of skin arranged in two rows under the
tongue called and what is their function?
Tony Booth
Grahamstown, South Africa
Out of puff: I have recently given up smoking and have developed a very
sore throat. Talking to other ex-smokers has revealed that they too were
afflicted with an increase in respiratory ailments when they gave up. More
bizarrely, a friend reported suffering from excessive flatulence on
quitting. Why, when you finally stop abusing yourself with nicotine, do
you suffer from symptoms that you didn鈥檛 previously experience?
K. Dupont
London
Nature鈥檚 gourmets: Why do humans cook their food? How long have they been
doing it? Does it really matter if you don鈥檛 eat food while it鈥檚 hot? On
balance, does cooking tend to increase or reduce the nutritional efficiency of
food? Are there any other creatures that need (or prefer) to modify the natural
state of their food in some way?
Glenn Wood
Wolverhampton, West Midlands
Paper chase: Did people make paper aeroplanes before the Wright brothers flew
and, if so, when were they first made?
C. Oates
by e-mail, no address supplied