Ask mr brain...all will be explained

PUBLISHED : Wednesday, 11 August, 1999, 12:00am
UPDATED : Wednesday, 11 August, 1999, 12:00am

Why do swallows and dragonflies fly low or near the ground before it rains? Sometimes swallows and groups dragonflies fly close to the ground.

These are signs that tell us it is going to rain soon.

Usually swallows and dragonflies fly around to catch the small flying insects which form their diet.

When it is about to rain, the moisture content of the air increases, making the wings of small insects wet.

Since their wings are wet, these insects cannot fly as high as usual and they are forced to stay close to the ground. Swallows and dragonflies which feed on these insects also have to fly at a lower level in order to catch them.

So when you see swallows flying low, get your umbrella ready.

Can a person with heart disease fly to the United States or Canada? JOANNE Maryknoll Convent School Heart disease is the name given to a range of disorders that affect the muscle or blood vessels of the heart. As a result the heart cannot pump blood properly or efficiently because of poor circulation caused by blockage or obstruction of the coronary arteries.

Heart disease can be caused by diet, excessive salt intake, heavy smoking, drinking or drug use. It can also be hereditary.

People with heart disease are often warned by their doctors not to fly. The reason for this is that even when pressurised during flight, aircraft cabins have lower levels of oxygen and lower air pressure than at sea level.

Oxygen deprivation during flights is a big problem for people with heart problems, especially on the long journey to the United States.

The reduced oxygen and air pressure increase the burden on the heart and can endanger the patients' lives.

For the same reason people with heart disease are recommended to check with their doctors before going to high altitude places such as Tibet or Nepal because of the lower levels of oxygen at high altitudes.

Some heart disease patients can fly as long as they consult their doctor closely and follow medical advice.

If necessary, most airlines provide inflight oxygen for a charge.

What are the differences between shortsightedness and longsightedness? Shortsightedness is an eye defect whereby near objects are clear and distant objects are blurred because the eyeball is too long or the refractive power of the eye is too strong. Longsightedness is the opposite problem, so near objects appear blurred but distant objects can be seen clearly. This usually occurs when the eyeball is too short or the eye's refractive power is too weak.

In shortsightedness, the image is focused in front of the retina of the eye rather than on it, whereas in longsightedness the image is focused behind the retina.

Glasses with a concave lens can compensate for shortsightedness and convex lenses correct longsightedness.