This is a simple experiment to measure the "specific heat" (also called "specific heat capacity") of any fluid. In addition to the principle of specific heat, the experiment also demonstrates some basic electrical principles such as Ohm's law.
Specific heat is typically quoted in units of J/g/K or J/g/degreeC (Joules per gram per Kelvin or Joules per gram per degree Celcius). For example, if a substance has a heat capacity of 2 J/g/degreeC that means it takes 2 Joules of energy to raise the temperature of 1 gram of the substance by 1 degree Celcius. Note that when we are talking about temperature changes rather than absolute temperatures, a Kelvin is the same as a degree Celcius.
Why would you want to know the specific heat of a fluid? Well, suppose you want to Build your own flat panel solar thermal collector
and you'd like to find or create a fluid that can store lots of energy for a small change in temperature. You might want to experiment with different fluid compositions to see what has the highest specific heat.