Lally's Law is a principle in the field of physics that describes the relationship between the pressure and volume of a gas. It states that for a given amount of gas at a constant temperature, the product of its pressure and volume remains constant. This means that if the volume of the gas decreases, its pressure increases, and vice versa. This law is a specific case of the more general ideal gas law. The law is named after John Lally, who contributed to the understanding of gas behavior in the 19th century. Lally's Law is often used in various applications, including engineering and meteorology, to predict how gases will behave under different conditions. Understanding this law helps in designing systems that involve gas compression and expansion.