**** Info via Environment Canada
Heat, humidity and your hair!
Have you noticed that on hot, humid days, your hair changes? Those with naturally curly hair see their hair become “frizzy” and those with fine, straight hair notice that their locks become limp. Well, you can blame it all on the weather!
The reason is that hair is hygroscopic or water-absorbing, meaning that hair strands are able to absorb and then release water molecules with and into the surrounding air. Essentially, strands of hair lengthen when the humidity increases, and then contract again when the humidity decreases. The rate of change in the length of hair strands is so dependable that hair strands were originally used as a key part of a hair hygrometer – a meteorological instrument used to measure the moisture level in the air!
A hair hygrometer measures relative humidity by monitoring the variation in length of a strand of human hair. Credit: US Weather Bureau (renamed US National Weather Service in 1954) and National Museum of American History.
Leonardo da Vinci first thought of inventing an instrument to measure the air’s humidity level. He built the first known hygrometer in 1480, which resembled a scale: on one plate, a tiny slither of non-absorbent wax was placed, and on the other side, an absorbent piece of cotton was placed. The humidity of the atmosphere was determined by measuring the imbalance caused by the absorption of moisture by the cotton, which, when dry, was equal to the weight on the other side of the scale.
An early version of a hygrometer. Source: Leonardo da Vinci Museum. Rome, Italy.
Why do we need to measure humidity?
moisture levels in the atmosphere, but in the summer months, the higher the humidity, the warmer the ambient air temperature feels. High humidity in the summer can make it feel uncomfortably hotter than the air temperature would suggest. In this case, we use “feels like” temperature reading, also known as the “humidex”, to help us make a better assessment of the conditions outdoors. The humidex is a calculated number – not measured – and therefore has no °C unit. Note that our forecasts indicate “feels like” temperatures only when the air temperature is above 25°C.
