A nervy time in make-up QUESTION When we acted daft, why did my gran say we were ‘Doolally tap’?
QUESTION Why is it almost impossible to apply mascara without opening your mouth?
NeuroscieNtists suspect it is a case of crossed nerve wires.
so-called mascara mouth is the familiar wide-jawed look adopted as we try to keep our eyelids still and so avoid a painful jab in the eye, while applying the cosmetic to lashes.
the cause appears to be an interaction between the trigeminal, facial and oculomotor nerves.
the mandibular branch of the trigeminal nerve controls the movement of muscles in the jaw. the facial and oculomotor nerves together control the movement of eyeballs and eyelids.
the three nerves originate in close proximity in the brainstem and it’s thought they may be triggered together by the action of applying mascara.
it is believed a similar mechanism causes the photic sneeze reflex — sneezing when exposed to bright sunlight.
A sneeze is usually triggered by an irritation in the nose, which is sensed by the trigeminal nerve. the root of this nerve is close to the optic nerve, which senses light entering the retina.
As the optic nerve fires to signal the brain to constrict the pupils, the electrical signal is sensed by the trigeminal nerve and mistaken by the brain as an irritant in the nose.
Suzanne Holden, Edinburgh.
QUESTION Has China’s Three Gorges Dam slowed down the Earth’s rotation?
the three Gorges Dam on the Yangtze river in china is the largest hydroelectric dam on the planet.
By holding 42 billion tons of water 575ft above sea level, it alters the earth’s moment of inertia and slows it down — a little. Nasa has calculated it increases the length of a day by 0.06 microseconds.
the moment of inertia is a measure of how resistant an object is to changes in its rotational motion about a given axis. the further the distance of a mass from its axis of rotation, the slower it will spin.
A good example is a spinning ice skater. When the skater extends their arms outwards, this increases the moment of inertia and the velocity of the spin decreases by a proportionate amount.
to increase the velocity of the spin, the skater must tuck in their arms to decrease the moment of inertia. similarly, to somersault faster, a diver will bring his body into a tucked position. Chris Wordsworth, York.
Further to the earlier answer about the excessive heat and boredom of Deolali transit camp in Maharashtra, my father served in the British Army in india in the 1930s and often used the phrase.
he’d tell stories about soldiers who had gone ‘Doolally tap’, including one who painted his dog green and another who rented bicycles so he could crash them.
Trevor Masters, Bradford. IS THERE a question to which you want to know the answer? Or do you know the answer to a question here? Write to: Charles Legge, Answers To Correspondents, Daily Mail, 2 Derry Street, London W8 5TT; or email charles.legge@dailymail.co.uk. A selection is published, but we’re unable to enter into individual correspondence.