Without considering all dependent parameters, we cannot reach a conclusion that brass shrinks on heating. Due to heat, during hot summer day, metals tend to expand. The coefficient of expansion differs from metal to metal. As the coefficient of linear expansion of aluminium is more than brass, it will expand comparatively more. As a result there will be an apparent decrease in length of the brass rod, as measured by the aluminium scale. It is not that brass shrinks on heating instead we can say on heating, aluminium expands more than brass.