Solids do not expand very much and so we have to find a way of magnifying this expansion. You can do this in the laboratory with a bar of iron or steel and a slide projector. The bar is fixed in a retort stand and the end of the bar is placed so that it sticks into the beam of the projector where the slide carrier would have been. The shadow of the bar is focused onto a wall on the other side of the laboratory.
The bar is now heated strongly in a Bunsen flame and you will see the shadow grow. If you measure the width of the bar and the shadow you can work out the magnification of the projector and then the actual expansion of the bar.