"A raised weight can produce work, but in doing so it must necessarily sink from its height, and, when it has fallen as deep as it can fall, its gravity remains as before, but it can no longer do work"

This quote by Hermann von Helmholtz is referring to the principle of energy and how it is used to do work. The quote is stating that when a weight is raised, it can be used to do work, however in the process of doing so, it will lose energy and eventually fall to its floor. At this point, the weight still has its gravity, but it can no longer do work since it has actually lost all of its energy. This quote is highlighting the value of energy and how it is required for work to be done. It also highlights the concept that energy is not unlimited and can be used up, which is why it is necessary to save energy whenever possible.