Students build thermometers.

As described in this post, I like to have students build “instruments” to measure the most oceanographic properties (temperature, salinity and density). I find that they appreciate oceanographic data much more once they have first-hand experience with how difficult it is to design instruments and make sense of the readings. Over the last two days I described the experiments for salinity and density, today it’s temperature.

Students building thermometers.

Measuring temperature is probably the most difficult of the three properties. Firstly, there are lots of technical difficulties to be overcome. How can we seal the mouth of the bottle around the straw in a way that it is really water tight? How much water do we have to fill in the bottle? Does it matter if there are air bubbles trapped? What if the water level when we fill the bottle is not visible because of the seal? If the straw is clogged up with modeling clay, will we still be able to use it in the instrument? How long does the straw have to be above the seal in order to avoid water spilling out when the temperatures we try to measure become too hot?

Then, there are many problems connected to the actual measurement. If we lift up the thermometer (and hence squeeze the plastic bottle) – how does that influence our reading? Since we have half a liter of water in the thermometer, are we actually measuring the temperature of the water sample, or are we influencing it while trying to measure? How do we come up with a scale for our temperature measurements had I not supplied (mercury-free) thermometers to calibrate the new thermometer with? So many questions to think about and discuss!