A barometer is an instrument for measuring the pressure of the air, due to the weight of the column of air above it. As the earth’s atmosphere gets thinner with increasing height, it follows that as we ascend from sea level and low-lying parts of the earth’s surface, the weight of the air will decrease. That is, the pressure will fall. An ordinary clock face type barometer placed in your car will give an estimate of the changes in altitude as you drive through the country. If we use rough figures, we can say that the reading decreases by three hectopascals for each twenty-five … [Read more...]