As the result of Andrews' experiments on the boiling-points of substances, we have the law enunciated that There is a critical temperature for every vaporous or gaseous substance ; such that, only when its temperature is below this, can the substance be reduced to the liquid form by any pressure, however great. Similarly, a law may be laid down regarding the passage from the liquid to the solid state, or vìce versâ. Thus we may say that There is a critical temperature for every solid substance, which contracts in the act of liquefaction, such that only when its temperature is above this, can the substance be reduced to the liquid form by any pressure, however great; and for every liquid substance, which contracts in the act of solidification, such that only when its temperature is below this, can the substance be reduced to the solid form by any pressure, however great.